Why a w9 form is needed for security deposit

[Michael Orlando]

Hello BP community. My question is about security deposits. So in pa you need to keep security deposits in an escrow account. So I go to my bank and they say all they need from the tenants is a w9 form. The one tenant asks why they need to provide it. Im not sure why they need to and the bank just said because it’s their money. Does anyone have a more detailed explanation on why the tenants would have to provide this? Thanks for your time.