Water usage and billing tenants

[Justin Davis]

Does anyone know the best way to charge tenants, at a triplex on one water bill? I have a tenant with five kids. I live in another unit and another guy lives in the other. That's a total of 8 occupants using the water. It wouldn't be fair to split it 3 ways, equally. I was thinking usage. That brings me to my next question. Does anyone know an affordable way to measure their usage? I do not want to charge a fee because I have to count that as income. Thank you in advance.