Our lease states we paid a $500 pet fee when we moved in, but doesn't say what it is used for. Is an explanation required in WA?

The requirement is that they call it a fee, and tell you that they are not refunding it under any circumstances, What they do with that fee is irrelevant. It isn't a deposit, they don't have to account for it. Not sure where you got the idea that if you are charged a pet fee they are required to tell you what they are using it for. The fee is theirs- in consideration of allowing you to bring in your pet, and there is no explanation required other than the requirement that they tell you that it is not a deposit and they are not going to return it. Elizabeth Powell

I agree with Elizabeth's answers above. However, I'd like to point out in addition that a landlord's acceptance of a fee may limit his or her ability to recover for damages. For example, RCW 59.18.130(10) removes a tenant's liability for "normal cleaning" when the landlord collects a "nonrefundable cleaning fee." This section probably won't apply to a "pet fee" unless there is a term in the lease that designates the pet fee for cleaning. Does a pet fee have to be applied to charges from the landlord for damages caused by the pet? I can imagine legal arguments from both sides of this issue. The landlord argument might be that the fee was collected in consideration of permission to house the pet and therefore it was fully earned at the time of payment and doesn't need to be applied to anything. The tenant's argument could be that the fee is a payment in anticipation of damages from the pet and therefore it should be applied to the actual damages claimed by the landlord. Even more boldly, a tenant might be able to argue in some cases that the pet fee in a badly worded lease is a liquidated damages clause and that the landlord should not be able to collect for damages in excess of it. As is usual, a careful reading of the lease is very important. In my experience, landlords tend to apply the fee to any pet cleaning or damages. If they don't and charge for cleaning/damages in addition to the fee, an attorney might be able to get them to change their minds.