Can a Washington landlord deduct from the deposit for pet damage?

Yes, but only for actual damage caused by the pet, not for the existence of the pet itself. Pet-attributable damage includes: chewed door frames or moldings, urine staining of carpets that requires replacement (not just cleaning), scratched hardwood floors, holes in walls from pets, or odor remediation. The deduction must reflect actual cost (with invoice) or reasonable estimate, and the damage must be documented with photos. Excluded as not deductible: routine cleaning, light pet hair, minor scratches that fall within normal wear, or "pet rent" amounts that were already pre-paid. If the tenant paid a separate non-refundable pet fee, that fee covers some or all of the routine pet impact and may reduce what can be deducted from the security deposit. Up to 2x the wrongfully withheld amount plus attorney fees under RCW 59.18.280(2).

Source: RCW 59.18.280