Is a pet deposit separate from the security deposit in Washington?

Sometimes, but the total still counts toward the Washington cap of no statewide cap in Washington. If the deposit is refundable (returned at end of tenancy minus any pet-caused damages), it is part of the security deposit and counts toward the cap. If it is structured as a non-refundable pet fee (one-time charge clearly labeled non-refundable in the lease), most Washington jurisdictions allow it outside the deposit cap, but the lease must be explicit. Pet rent (a recurring monthly charge) is also generally allowed and is not part of the deposit. The treatment varies by state. Mixing refundable and non-refundable pet charges in the same line of the lease is a common drafting error that gets the entire amount treated as deposit. Up to 2x the wrongfully withheld amount plus attorney fees under RCW 59.18.280(2).

Source: RCW 59.18.280