Inherited Bad Lease - Need Some Guidance

[Nick Jax]

Hello,

I purchased a property with 3 apartments and 1 store.  There is only 1 water meter on the property, so I pay the water bill (working on that..). I inherited the leases of all 4 tenants.

The store lease states I pay the water bill but they agree to pay anything over what is considered NORMAL.  However the previous LL didn't bother to define NORMAL.  I'm not even sure myself how to make this determination as how do I know it's not an apartment using more water than anyone else?  I've considered sub-metering, but that's down the road.  For right now, is there any fee I can apply LEGALLY? 

Thanks.