Water bill dispute (one water meter for Duplex)

[Max Matsuk]

Good Afternoon all.

we have a situation where our landlord came to us 6 months after the signed lease to demand a monthly payment of the water bill. In the contract it states that we are responsible for all utilities, and we have no problem paying our share. BUT, the water is metered by one meter, (This was not specified in the lease) we want to pay for only what we use since we are almost never home. what is the best way to go about this?? 

Thanks in advance