On-site Washer and Dryer

[Felicia Stafford]

I just purchased a 3 family.  The 1st and 2nd floor have washer and dryer hook-ups in the basement (tenants supply their own machines).  

The 3rd floor does not have a hook-up, but there is space for it. I am considering asking the tenant if they want the hook-up and are willing to get their own washer and dryer.  If they say yes, I'll have to adjust the rent which the previous owner kept low because it did not have this benefit.  How much should I adjust the rent for the additional water use?