some laundry faucet has a pipe connect to it at the back and when you open that faucet, it will fill some water from that pipe into your floor drain. i had one of that kind and when the faucet washer worn out, it started leaking from that pipe into floor drain. big $ bill
the same for my family?! I checked everywhere but didn't find any leaking place . I thought maybe the last time reading was wrong, which is smaller then usual.