Shared water bill on a duplex

[Ben M.]

One of the tenants in a duplex with a shared water meter is complaining that he should pay lesser than the other tenant because he doesn’t use the water that much. They are supposed to half the bill per the contract. I know I can say that he has to pay half per the contract but I do see the unfairness in this situation. I’m thinking of just taking over part of the payment and just have them pay a fixed monthly payment but has anyone else run into this issue and how did you handle it? Thank you