WIGGINS, J.
*696¶ 1 We decide here two important aspects of the work product doctrine. First, were the e-mails exchanged between the Kittitas County and the Department of Ecology work product? Second, if the e-mails are work product, are they discoverable under the *1236Public Records Act (PRA), chapter 42.56 RCW? We hold that the e-mails are work product because they were prepared by or for Kittitas County in anticipation of litigation. Second, we hold that Kittitas County did not waive its work product protection because disclosure of the e-mails to Ecology never created a significant likelihood that an adversary would also obtain the information. As a result, we affirm the Court of Appeals.
FACTS AND PROCEDURAL HISTORY1
I. Enforcement Action
¶ 2 Chem-Safe Environmental is a hazardous waste facility located in Kittitas County. Clerk's Papers (CP) at 2002.
*697While inspecting a neighboring facility, James Rivard, the Kittitas County environmental supervisor, and Gary Bleeker, an Ecology employee, saw drums labeled as hazardous waste on property belonging to Chem-Safe and ABC Holdings. Id. 2000, 2002. Upon investigation, Rivard learned that Chem-Safe did not hold a permit to handle or store moderate risk waste. Id. at 2002.
¶ 3 Throughout the next two years, both Kittitas County and Ecology employees visited the Chem-Safe facility together, e-mailed one another about the matter, and met to discuss the progress in bringing Chem-Safe into compliance with state and local regulations. Id. at 2002-08. Chem-Safe never satisfied Kittitas County's or Ecology's requirements regarding operation of its facility. Id. at 2008.
¶ 4 Eventually, Kittitas County issued a "Notice of Violation and Abatement" (NOVA) requiring Chem-Safe to halt operations until it obtained the necessary permits and equipment and conducted contamination testing. Id. at 2009, 1265-68. The NOVA cover letter discussed the work of both Kittitas County and Ecology on the case and listed both as resources from which Chem-Safe could receive technical assistance to meet the NOVA's requirements. Id. at 1265.
¶ 5 Chem-Safe appealed the NOVA, which was affirmed by a hearing officer. Id. at 1273-79. Chem-Safe then appealed the hearing officer's ruling, which was subsequently affirmed by the superior court and the Court of Appeals. Id. at 1281-88; ABC Holdings, Inc. v. Kittitas County, 187 Wash. App. 275, 348 P.3d 1222 (2015). We denied review of the appellate court decision. ABC Holdings, Inc. v. Kittitas County, 184 Wash.2d 1014, 360 P.3d 817 (2015).
¶ 6 During the course of the litigation, Kittitas County deputy prosecutors sent several e-mails back and forth to Ecology employees. In one of those e-mails, an Ecology employee e-mailed a county deputy prosecutor, asking, "Should these emails be considered attorney-client privileged ?" CP at 1501 (emphasis added). The Kittitas County deputy prosecutor *698responded, "[Ecology] is not my client (Kittitas County is), therefore, these e-mails are not attorney-client privileged. " Id. at 1500 (emphasis added). The Kittitas County deputy prosecutor copied her response to an assistant attorney general. Id. The assistant attorney general also responded, stating that the e-mails were not attorney-client privileged without a joint-prosecution agreement. Id. at 1499. The assistant attorney general also stated that there might be other privileges that applied to the e-mails but that she lacked enough information to know the specific options for keeping the e-mails privileged. Id. at 775. Thus, the record reflects only the parties' understanding of whether Kittitas County and Ecology's communications with one another were attorney-client privileged.2 *1237II. Public Records Action
¶ 7 Against this backdrop, and while the Court of Appeals reviewed the NOVA, Sky Allphin, president of Chem-Safe, filed a PRA request with Kittitas County. Id. at 2001, 70. Allphin requested all records from January 1, 2010, forward relating to the inspection of Chem-Safe's facility and specifically requested correspondence from Kittitas County, Ecology, and other agencies. Id. at 70. Ultimately, Kittitas County produced more than 20,000 pages of records in monthly increments. Id. at 1108-14.
¶ 8 Allphin also filed a similar PRA request with Ecology. Id. at 71. Five days later, in response to a request from Kittitas County, Ecology "promised to withhold the records"
*699while Kittitas County sought an injunction.3 Id. at 2695-96, 2718 ("The Ecology public records officer promised that such records would not be released until [Kittitas] County had an opportunity to seek court protection as allowed by RCW 42.56.540 and 42.56.550."). Kittitas County sought, and the superior court granted, a temporary restraining order to prevent the release of several e-mails that Kittitas County claimed to be exempt from production as work product under the PRA. CP at 92-96, 661-67. Allphin disputed whether these e-mails were work product and, if so, whether Kittitas County had waived any accompanying privilege. Eventually, the parties narrowed down the list of disputed records to 32 e-mail chains. Id. at 781, 2722-24.
¶ 9 The superior court held an in camera review of the e-mail chains claimed exempt by Kittitas County. Id. at 781. After its review, the court determined the e-mails were exempt from production under the PRA as work product, enjoined Ecology from releasing the e-mails, and sealed them. Id. at 789. The court then granted summary judgment in favor of Kittitas County, holding that Kittitas County did not violate the PRA. Id. at 2978-83.
¶ 10 Allphin, Chem-Safe, and ABC Holdings (collectively Chem-Safe) appealed the superior court's grant of summary judgment and sealing of the e-mails. The Court of Appeals affirmed the superior court in a partially published opinion. See Kittitas County v. Allphin, 195 Wash. App. 355, 381 P.3d 1202 (2016).
¶ 11 The Court of Appeals concluded that the e-mails exchanged between Kittitas County and Ecology were work product because they "contain statements of fact and legal strategies prepared by and for the various employees of [Kittitas] County and Ecology in response to the Chem-Safe litigation." Id. at 366-67, 381 P.3d 1202. It further concluded that "the two agencies agreed to undertake a joint/common cause in the *700regulatory enforcement litigation against Chem-Safe" and, thus, the work product protection in the e-mails was not waived by disclosure to Ecology because of the common interest doctrine. Id. at 369-70, 381 P.3d 1202.
¶ 12 Chem-Safe filed a petition for review of the Court of Appeals decision with this court. We partially granted the petition on the issue of whether the common interest doctrine applied to the e-mails exchanged between Kittitas County and Ecology, exempting the documents from production under the PRA as work product.
STANDARD OF REVIEW
¶ 13 We review challenges under the PRA de novo. RCW 42.56.550(3). Our review of summary judgment motions is also de novo. Scrivener v. Clark Coll., 181 Wash.2d 439, 444, 334 P.3d 541 (2014). "Summary judgment is appropriate only when there is no genuine issue as to any material fact and the moving party is entitled to judgment as a matter of law." Id. ; see also CR 56(c).
ANALYSIS
¶ 14 We first conclude that the e-mails exchanged between Kittitas County and Ecology are work product. Next, we adopt the rule, used by both federal and state courts, that a party waives its work product protection when it discloses work product *1238documents to a third party in a manner creating a significant likelihood that an adversary will obtain the information. See 8 CHARLES ALAN WRIGHT ET AL., FEDERAL PRACTICE AND PROCEDURE: CIVIL § 2024 (3d ed. 2010). Using this rule, we conclude that Kittitas County did not waive its work product protection by exchanging e-mails with Ecology employees. As a result, the e-mails are not subject to disclosure under the PRA.4 *701I. The E-mails Are Work Product
¶ 15 We hold that the e-mails exchanged between Kittitas County and Ecology constitute work product. The e-mails were prepared by or for Kittitas County in anticipation of litigation over the NOVA. As a result, they qualify as work product under Civil Rule (CR) 26(b)(4).
A. The PRA and the Controversy Exception
¶ 16 "The primary purpose of the PRA is to provide broad access to public records to ensure government accountability." City of Lakewood v. Koenig, 182 Wash.2d 87, 93, 343 P.3d 335 (2014). An agency must disclose responsive public records "unless the record falls within the specific exemptions of [the PRA] ... or other statute." RCW 42.56.070(1). "Consistent with its purpose of disclosure, the PRA directs that its exemptions must be narrowly construed." Koenig, 182 Wash.2d at 94, 343 P.3d 335 ; see also RCW 42.56.030.
¶ 17 Here, Kittitas County claimed an exception from PRA disclosure under RCW 42.56.290, commonly referred to as the "controversy exception." See Soter v. Cowles Publ'g Co. , 162 Wash.2d 716, 732, 174 P.3d 60 (2007) (plurality opinion). That exception states,
Records that are relevant to a controversy to which an agency is a party but which records would not be available to another party under the rules of pretrial discovery for causes pending in the superior courts are exempt from disclosure under [the PRA].
RCW 42.56.290. The standard for determining whether records would be discoverable in superior court is CR 26. Limstrom v. Ladenburg, 136 Wash.2d 595, 600-01, 963 P.2d 869 (1998) (holding that "a citizen has the right to inspect documents ... unless the documents requested would not be available to a party under the discovery rules set forth in *702the civil rules for superior court"). Here, Kittitas County claims that under CR 26(b)(4), the e-mails qualify as work product and thus are exempt from disclosure under the controversy exception.5
B. Work Product
¶ 18 The work product doctrine originates from the United States Supreme Court case Hickman v. Taylor , 329 U.S. 495, 67 S.Ct. 385, 91 L.Ed. 451 (1947). In Hickman, most of the crew of a tugboat died when it sank. Id. at 498, 67 S.Ct. 385. The representative of one of the deceased sued the owners of the tugboat. Id. Prior to the lawsuit, the owners' attorney made notes of interviews with the surviving crew and others with relevant knowledge about the accident. Id. During discovery, the plaintiff sent the defendants interrogatories asking them to produce all the statements that they had taken about the event. Id. at 498-99, 67 S.Ct. 385. The defendants refused to produce the notes and interviews taken by their attorney and were held in contempt. Id. at 499-500, 67 S.Ct. 385. They appealed, and the Court of Appeals reversed. Id. at 500, 67 S.Ct. 385. The Supreme Court granted certiorari and affirmed the Court of Appeals, holding that the work product of attorneys was protected from discovery by an adversary. Id. at 509-10, 67 S.Ct. 385.
¶ 19 First, the Supreme Court distinguished between attorney work product and materials that are privileged under the attorney-client privilege. Id. at 508, 67 S.Ct. 385. It noted that the scope of the attorney-client *1239privilege did not protect information collected from a witness by an attorney acting on behalf of his or her client. Id. The Court also stated that the attorney-client privilege did not extend to materials prepared by an attorney for his or her use in prosecuting a case or to materials that "reflecte[d] an attorney's mental impressions, conclusions, opinions or legal theories." Id. *703¶ 20 After drawing this distinction, the Supreme Court went on to establish the importance of protecting an attorney's files and mental impressions. Id. at 510, 67 S.Ct. 385. The Court reasoned that more harm than good would result from allowing such discovery:
Were such materials open to opposing counsel on mere demand, much of what is now put down in writing would remain unwritten. ... Inefficiency, unfairness and sharp practices would inevitably develop in the giving of legal advice and in the preparation of cases for trial. The effect on the legal profession would be demoralizing. And the interests of the clients and the cause of justice would be poorly served.
Id. at 511, 67 S.Ct. 385.
¶ 21 The protection of an attorney's work product is not without limitation. The Supreme Court noted that attorney documents containing relevant, nonprivileged facts were discoverable under certain circumstances, such as when witnesses are no longer available. Id. The Court was careful to note that even in these circumstances, the burden rests on the party seeking production to "establish adequate reasons to justify production through a subpoena or court order." Id. at 512, 67 S.Ct. 385.
¶ 22 Washington has a similar work product protection rule, which is codified in CR 26(b)(4) :
[A] party may obtain discovery of documents and tangible things ... prepared in anticipation of litigation ... only upon a showing that the party seeking discovery has substantial need of the materials in the preparation of such party's case and that party is unable without undue hardship to obtain the substantial equivalent of the materials by other means. In ordering discovery of such materials when the required showing has been made, the court shall protect against disclosure of the mental impressions, conclusions, opinions, or legal theories of an attorney or other representative of a party concerning the litigation.
See also Heidebrink v. Moriwaki , 104 Wash.2d 392, 396, 706 P.2d 212 (1985). As a result, "[t]he work product doctrine *704does not shield records created during the ordinary course of business," but applies only to those materials prepared in "anticipation of litigation." Morgan v. City of Federal Way , 166 Wash.2d 747, 754, 213 P.3d 596 (2009). The "determination of whether material was prepared in the anticipation of litigation in a particular case, and thus qualifies as work product, requires examination of the specific parties and their expectations." Harris v. Drake, 152 Wash.2d 480, 487, 99 P.3d 872 (2004). The litigation may be " 'completed, existing, or reasonably anticipated.' " Soter, 162 Wash.2d at 732, 174 P.3d 60 (quoting Dawson v. Daly, 120 Wash.2d 782, 791, 845 P.2d 995 (1993), overruled on other grounds by Soter, 162 Wash.2d at 755, 174 P.3d 60 ). When creating work product in anticipation of litigation, "there is no distinction between attorney and nonattorney work product." Heidebrink, 104 Wash.2d at 396, 706 P.2d 212.
¶ 23 Pursuant to this rule, we have established some specific guidelines regarding when an attorney's work product is discoverable:
(1) The mental impressions of the attorney and other representatives of a party are absolutely protected, unless their mental impressions are directly at issue. Pappas v. Holloway, 114 Wn.2d 198, 212, 787 P.2d 30 (1990).
(2) The notes or memoranda prepared by the attorney from oral communications should be absolutely protected, unless the attorney's mental impressions are directly at issue. See Pappas, 114 Wn.2d at 212 [787 P.2d 30] ; Dever v. Fowler, 63 Wn. App. 35, 48, 816 P.2d 1237 (1991).
(3) The factual written statements and other tangible items gathered by the attorney and other representatives of a party are subject to disclosure only upon a showing that the party seeking disclosure of the documents actually has substantial need of *1240the materials and that the party is unable, without undue hardship, to obtain the substantial equivalent of the materials by other means, Mental impressions of the attorney and other representatives embedded in factual statements should be redacted. Heidebrink, 104 Wn.2d 392 [706 P.2d 212].
Limstrom, 136 Wash.2d at 611-12, 963 P.2d 869 ; see also Lewis H. Orland, *705Observations on the Work Product Rule, 29 GONZ. L. REV . 281 (1994). We have further described the scope of work product as follows:
The civil work product protection applies to documents and other tangible things that (1) show legal research and opinions, mental impressions, theories, or conclusions of the attorney or of other representatives of a party; (2) are an attorney's written notes or memoranda of factual statements or investigation; and (3) are formal or written statements of fact, or other tangible facts, gathered by an attorney in preparation for or in anticipation of litigation.
Limstrom, 136 Wash.2d at 611, 963 P.2d 869.
¶ 24 For example, in Soter, we held that the notes of a school district's attorney and the notes of an investigator hired by that attorney were work product. 162 Wash.2d at 744, 174 P.3d 60. The attorney and investigator took the notes as part of the school district's investigation into the death of a child on a field trip. Id. at 722, 174 P.3d 60. The parents of the child sued the school district, and a newspaper filed a public records request with the school district, asking for the notes taken during the investigation. Id. at 723, 174 P.3d 60. The school district resisted production, asserting that the notes were work product and exempt from disclosure under the PRA controversy exception. Id. When deciding whether the notes were work product, we looked to the nature of the documents, whether those documents were prepared in anticipation of litigation, and whether the documents revealed "the attorneys' and investigator's thoughts regarding client and witness interviews." Id. at 743, 174 P.3d 60. We concluded that the notes were created in anticipation of litigation over the child's death and they reflected the attorneys' and investigator's thoughts about the litigation. Id. at 743, 744 n.13, 174 P.3d 60. Consequently, we held that the notes were work product.
¶ 25 Here, Chem-Safe argues that Soter relied on the fact that the school district hired the investigator, while here, Kittitas County did not hire Ecology. As a result, Chem-Safe asserts that the e-mails written by Ecology employees cannot be work product. However, Chem-Safe's characterization *706of Soter is incorrect. In Soter, we did not conclude that the investigator's notes were work product because the investigator had been hired by the school district. Instead, we focused on whether the notes "reveal[ed] what information the attorney deemed particularly important and, conversely, what the attorney did not find important enough to record." Id. at 743-44, 174 P.3d 60. As a result, because the "notes reflect[ed] the attorneys' and investigator's thoughts regarding client and witness interviews," we concluded that they were work product. Id. at 743, 174 P.3d 60.
¶ 26 Here, as in Soter, all the e-mails were created in anticipation of litigation and reflect attorney opinions, thoughts, and conclusions about the litigation. Thus, the emails are work product. The e-mail chains all include one or more of the following elements: (1) discussion of litigation-related technical, factual, and regulatory issues;6 (2) draft declarations with edits and notes;7 and/or (3) analysis of the risks of different litigation positions in the Chem-Safe lawsuit.8 All of these e-mails were created for investigative purposes or in pursuit of Kittitas County's litigation strategy surrounding the NOVA. Consequently, the e-mails contain "legal research and opinions, mental impressions, *1241theories, or conclusions," as well as "written notes or memoranda of factual statements or investigation" regarding the NOVA litigation. Limstrom, 136 Wash.2d at 611, 963 P.2d 869. The e-mails were prepared directly by Kittitas County's deputy prosecutors or included material prepared by Ecology representatives at the request of, and in support of, the deputy prosecutors. See Heidebrink, 104 Wash.2d at 396, 706 P.2d 212 (concluding "there is no distinction between attorney and nonattorney *707work product").9 Thus, the e-mails were created "by or for" Kittitas County to use in the Chem-Safe litigation. See CR 26(b)(4). As a result, they constitute work product under CR 26(b)(4) and are not discoverable unless the work product protection has been waived by Kittitas County.10
II. Waiver of Work Product Protection
¶ 27 Having concluded that the e-mails are work product, we must now decide whether Kittitas County waived its *708work product protection. Washington has yet to define a clear rule governing waiver of work product protection. See Limstrom v. Ladenburg, 110 Wash. App. 133, 144, 39 P.3d 351 (2002) ("Absent Washington case law on waiver of work product immunity, we look to other jurisdictions."). We now adopt the rule that a party waives its work product protection when it discloses work product documents to a third party in a manner creating a significant likelihood that an adversary will obtain the information. Using this rule, we hold that Kittitas County did not waive its work product protection.
A. Waiver in the Work Product Protection Context
¶ 28 A party waives its work product protection when "the client, the client's lawyer, or another authorized agent of the client ... discloses the material to third persons in circumstances in which there is a significant likelihood that an adversary or potential adversary in anticipated litigation will obtain it." RESTATEMENT (THIRD) OF THE LAW GOVERNING LAWYERS § 91(4) ( AM. LAW INST . 2000). This is the rule used by both federal and other state courts. See, e.g., In re Chevron Corp., 633 F.3d 153, 165 (3d Cir. 2011) ("[l]t is only in cases in which the material is *1242disclosed in a manner inconsistent with keeping it from an adversary that the work-product doctrine is waived."); O'Boyle v. Borough of Longport, 218 N.J. 168, 193, 94 A.3d 299 (2014) (" '[l]t is only in cases in which the material is disclosed in a manner inconsistent with keeping it from an adversary that the work-product doctrine is waived.' " (quoting In re Chevron Corp, 633 F.3d at 165 ) ); Am. Zurich Ins. Co. v. Thirteenth Judicial Dist. Court, 2012 MT 61, ¶ 26, 364 Mont. 299, 280 P.3d 240 ("Disclosure only waives work product protection if it is 'inconsistent with the maintenance of secrecy from the disclosing party's adversary.' " (quoting *709United States v. Deloitte LLP, 391 U.S. App. D.C. 318, 610 F.3d 129, 140 (2010) ) ).11 In clarifying a work product waiver rule, federal case law is persuasive since CR 26(b)(4) is nearly identical to Federal Rule of Civil Procedure 26(b)(3). See Soter, 162 Wash.2d at 739, 174 P.3d 60 ("Where a state rule is identical to its federal counterpart, analyses of the federal rule provide persuasive guidance as to the application of our comparable state rule.").
¶ 29 It is also illuminating to contrast the work product protection to the attorney-client privilege. The work product doctrine is designed to protect the efforts of an attorney and those who assist attorneys from disclosure to a litigation adversary. United States v. Am. Tel. & Tel. Co., 206 U.S. App. D.C. 317, 642 F.2d 1285, 1299 (1980) ("[T]he work product privilege does not exist to protect a confidential relationship, but rather to promote the adversary system by safeguarding the fruits of an attorney's trial preparations from the discovery attempts of the opponent. The purpose of the work product doctrine is to protect information against opposing parties, rather than against all others outside a particular confidential relationship, in order to encourage effective trial preparation." (emphasis and footnote omitted) ). By contrast, the attorney-client privilege is designed to protect the confidentiality of communications between attorney and client. Id. ("The attorney-client privilege exists to protect confidential communications, to assure the client that any statements he makes in seeking legal advice will be kept strictly confidential *710between him and his attorney; in effect, to protect the attorney-client relationship." (emphasis omitted) ).
¶ 30 Since the purposes of the work product doctrine and the attorney-client privilege are different, it should come as no surprise that standards for waiving attorney-client privilege and work product protection are also different. The work product protection permits disclosure to some, but not all, third parties:12
Effective trial preparation often entails disclosing work product to coparties and nonparties. Work product, including opinion work product, may generally be disclosed to the client, the client's business advisers or agents, the client's lawyer or other representative, associated lawyers and other professionals working for the client, or persons similarly aligned on a matter of common interest.
RESTATEMENT § 91 cmt. b. As a result, "while the mere showing of a voluntary disclosure to a third person will generally suffice to show waiver of the attorney-client privilege, it should not suffice in itself for waiver of the work product privilege." Am. Tel. & Tel. Co., 642 F.2d at 1299 (emphasis omitted).
¶ 31 In contrast, for the attorney-client privilege, "[t]he presence of a third *1243person during the communication waives the privilege." Morgan, 166 Wash.2d at 757, 213 P.3d 596 ; see also In re Pac. Pictures Corp., 679 F.3d 1121, 1126-27 (9th Cir. 2012) (noting "that voluntarily disclosing privileged documents to third parties will generally destroy the [attorney-client] privilege"); RESTATEMENT § 79 ("The attorney-client privilege is waived if the client, the client's lawyer, or another authorized agent of the client voluntarily discloses the communication in a nonprivileged communication."). *711¶ 32 The different standards of waiver for the attorney-client privilege and work product protection result from the differing purposes behind the doctrines:
The [attorney-client] privilege, it is said, is designed to protect confidentiality, so that any disclosure outside the magic circle is inconsistent with the privilege; by contrast, work product protection is provided against "adversaries," so only disclosing material in a way inconsistent with keeping it from an adversary waives work product protection.
United States v. Mass. Inst. of Tech., 129 F.3d 681, 687 (1st Cir. 1997). Compare Pac. Pictures, 679 F.3d at 1127 ("The reason behind [the attorney-client privilege waiver] rule is that, '[i]f clients themselves divulge such information to third parties, chances are that they would also have divulged it to their attorneys, even without the protection of the privilege.' " (internal quotation marks omitted) (second alteration in original) (quoting Comments, Stuffing the Rabbit Back into the Hat: Limited Waiver of the Attorney-Client Privilege in an Administrative Agency Investigation, 130 U. PA. L. REV . 1198, 1207 (1982) ) ), with Chevron Corp., 633 F.3d at 164-65 ("[T]he work-product doctrine protects an attorney's work from falling into the hands of an adversary, and so 'disclosure to a third party does not necessarily waive the protection of the work-product doctrine.' Rather, the purpose behind the work-product doctrine 'requires [a court] to distinguish between disclosures to adversaries and disclosures to non-adversaries[,]' and it is only in cases in which the material is disclosed in a manner inconsistent with keeping it from an adversary that the work-product doctrine is waived.") (citations omitted) (alterations in original) (quoting Westinghouse Elec. Corp. v. Republic of Philippines, 951 F.2d 1414, 1428 (3d Cir. 1991) ).13
*712¶ 33 For the foregoing reasons, we are persuaded that the rule adopted by both federal and state courts regarding the waiver of work product protection is sound and thus adopt it as the rule in Washington State.
B. Kittitas County Did Not Waive Its Work Product Protection
¶ 34 We turn now to whether Kittitas County created "a significant likelihood that an adversary or potential adversary in anticipated litigation" would obtain its work product when it exchanged e-mails containing work product with Ecology. RESTATEMENT § 91(4). We hold that Kittitas County did not waive its work product protection when the deputy prosecutors and Ecology employees exchanged e-mails about the NOVA litigation. The disclosures between Kittitas County and Ecology never created a circumstance in which it was significantly likely that Chem-Safe would be able to obtain the work product.
¶ 35 As discussed above, the work product doctrine permits parties to share work product in certain contexts without waiving the accompanying protections of the doctrine. See RESTATEMENT § 91 cmt. b. A party can share work product with coparties and others who are similarly aligned on a matter of common interests because such parties are unlikely to disclose work product to adversaries. Am. Tel. & Tel. Co., 642 F.2d at 1299 (holding that "with common interests *1244on a particular issue against a common adversary, the transferee is not at all likely to disclose the work product material to the adversary"). As a result, parties who share a common interest have a reasonable expectation of confidentiality. In re Subpoenas Duces Tecum, 238 U.S. App. D.C. 221, 738 F.2d 1367, 1372 (1984). *713¶ 36 The parties do not need a written agreement to maintain confidentiality in order for the work product protection to apply. "While [a written] agreement can serve as evidence of the parties' reasonable intent that information exchanged between those with a shared interest remain confidential, it should not be a prerequisite to the application of the common interest doctrine." Katharine Traylor Schaffzin, An Uncertain Privilege: Why the Common Interest Doctrine Does Not Work and How Uniformity Can Fix It, 15 B.U. PUB. INT . L. J. 49, 82-83 (2005). Instead, a reasonable expectation of confidentiality may derive from common litigation interests between the disclosing party and the recipient. Am. Tel. & Tel., 642 F.2d at 1299 ("with common interests on a particular issue against a common adversary, the transferee is not at all likely to disclose the work product material to the adversary"); see also Subpoenas, 738 F.2d at 1372.
¶ 37 Here, there are several factors demonstrating that Kittitas County and Ecology were "similarly aligned on a matter of common interest" and thus had a reasonable expectation of confidentiality. RESTATEMENT § 91 cmt. b. First, RCW 70.105.005 obliges Kittitas County and Ecology to cooperate on hazardous waste regulation. See RCW 70.105.005(10) (stating that "local government is the appropriate level of government to plan for and carry out programs to manage moderate-risk waste, with assistance and coordination provided by [Ecology ]" (emphasis added) ). Pursuant to this statutory direction, Kittitas County and Ecology worked together throughout the investigation into Chem-Safe's facility and throughout the appeal. CP at 2002-08. Kittitas County shared litigation strategy with Ecology and asked for its technical assistance on matters relating to the litigation. This common interest between Kittitas County and Ecology was more than a general interest in environmental standards or a mere shared desire to see a similar outcome in a legal matter. Instead, Kittitas County and Ecology shared a common legal interest to ensure that Chem-Safe *714complied with both local and state regulations regarding its operation of a hazardous waste facility.
¶ 38 Second, Kittitas County and Ecology cooperated over a period of several years. From 2008 to 2010, Kittitas County employees and Ecology employees visited the Chem-Safe facility together, e-mailed one another about the matter, and met to discuss the progress of bringing Chem-Safe into compliance. Id. at 2002-08. After the NOVA was issued and throughout 2011 and 2012, Kittitas County deputy prosecutors e-mailed Ecology employees to discuss litigation strategy and to request technical support on relevant factual matters related to the NOVA litigation. See id. at 781, 2724. The fact that Kittitas County and Ecology cooperated on the NOVA over a period of several years weighs in favor of a finding that they shared a common interest.
¶ 39 Third, Kittitas County and Ecology engaged in considerable sharing of work product. Although Kittitas County and Ecology did not have a formal confidentiality agreement, no written agreement to maintain confidentiality is required. Kittitas County employees e-mailed Ecology employees several times to discuss litigation-related technical, factual, and regulatory issues and the risks of different litigation positions in the Chem-Safe lawsuit. They also drafted declarations for the litigation, exchanging edits and notes on different versions. Such significant sharing of work product affirms Kittitas County and Ecology's intent to develop a common strategy to defend the NOVA in the related litigation.
¶ 40 Beyond the sharing of work product, there is evidence of other significant cooperation between Kittitas County and Ecology. Kittitas County employees and Ecology employees visited the Chem-Safe facility together several times while working to bring Chem-Safe into compliance with local and state hazardous waste regulations. Id. at 2002-08. Kittitas County employees and Ecology employees e-mailed one another and met together to discuss the *715ongoing issues at *1245Chem-Safe. Id. at 2002-08. The two also shared relevant information with one another regarding issues with Chem-Safe's compliance, such as a letter from the Idaho State Department of Environmental Quality about Chem-Safe. Id. at 2008. The NOVA cover letter referenced the participation of both Kittitas County and Ecology in investigating and working with Chem-Safe to resolve issues at its facility. Id. at 1265. This significant level of cooperation between Kittitas County and Ecology further evinces their common interest in the NOVA litigation.
¶ 41 As parties "similarly aligned on a matter of common interest," Kittitas County and Ecology had a reasonable expectation of confidentiality and thus did not waive work product protection by sharing e-mails back and forth. RESTATEMENT § 91 cmt. b.
C. Waiver of Work Product under the PRA
¶ 42 Despite the common interest between Kittitas County and Ecology, Chem-Safe argues that the PRA entitles it to obtain the e-mails from Ecology. We disagree.
¶ 43 As public agencies, both Ecology and Kittitas County are subject to required disclosures under the PRA. But, the PRA does not give an adversary the presumptive right to obtain work product. In fact, the opposite is true; the PRA specifically exempts work product from disclosure. RCW 42.56.290 ("Records that are relevant to a controversy to which an agency is a party but which records would not be available to another party under the rules of pretrial discovery for causes pending in the superior courts are exempt from disclosure under this chapter." (emphasis added) ). Because they are work product, the disputed e-mails "would not be available to another party under the rules of pretrial discovery for causes pending in the superior courts." Id; see CR 26(b)(4) (exempting work product from pretrial discovery unless a party shows undue hardship). And the scope of the work product protection is *716no different in a PRA setting than it is in a general civil litigation setting. Soter, 162 Wash.2d at 743, 174 P.3d 60 ("Moreover it is important to consider that while this case happens to be a public records case, when evaluating the extent of the protection offered by CR 26(b)(4), we are interpreting the civil discovery rule that applies to all civil cases. When we interpret the meaning of CR 26(b)(4) 's work product protection, we not only impact attorneys representing government agencies, but we will impact all attorneys engaging in civil practice."). It follows under RCW 42.56.290 that the e-mails are exempt from disclosure under the PRA.
¶ 44 "[A] litigant should not succeed in obtaining opinion work product that would be protected from discovery by [the civil rule] by seeking the opinion work product through a public records request." DaRosa v. City of New Bedford, 471 Mass. 446, 459, 30 N.E.3d 790 (2015). Under CR 26(b)(4), we allow the disclosure of work product only under narrow circumstances. For example, we permit disclosure when the mental impressions of the attorney are directly at issue or the party seeking disclosure has substantial need for factual information that he or she would be unable, without undue hardship, to obtain. Limstrom, 136 Wash.2d at 611-12, 963 P.2d 869. However, even under the latter situation, we still require that the mental impressions of the attorney be redacted. Id.
¶ 45 Here, Chem-Safe has not alleged that the mental impressions of the deputy prosecutors are at issue. Nor does Chem-Safe argue that it is entitled to the factual information contained in the e-mails based on undue hardship. As a result, Chem-Safe has not shown that it is entitled to disclosure of the e-mails under CR 26(b)(4), and the mere fact that it brings its request under the PRA does not entitle it to disclosure either.
¶ 46 In short, when Kittitas County sent the work product documents to Ecology, the documents did not lose their protection as work product; they remained exempt from discovery and therefore exempt from production under the *717PRA. See RESTATEMENT § 87(3) ("Except for material which by applicable law is not so protected, work product is immune from discovery or other compelled disclosure.").
CONCLUSION
¶ 47 We hold that the e-mails exchanged between Kittitas County and Ecology constitute *1246work product. All the e-mails were created by or for Kittitas County in anticipation of the litigation between Kittitas County and Chem-Safe over the NOVA. We also adopt the rule used by both federal and state courts for work product protection waiver and hold that Kittitas County did not waive its work product protection when it exchanged the e-mails with Ecology because disclosure of the emails to Ecology did not make it substantially likely that Chem-Safe would obtain the information. As a result, we affirm the Court of Appeals.
WE CONCUR.
Johnson, J.
Owens, J.
Stephens, J.
Gordon McCloud, J.