For septic you can register with the Texas PUC to pass through sewer charges based on the tenants water usage so all is not lost recovering the run & maintain charges.

Like interest rateMaybe consider $50/unit per month for water usage or 10% for vacancyRent amount via ?

They can call utility companies and ask for average usage over the past 12 months for an estimate.

The expenses of running an apartment property include vacancy loss, maintenance, repairs, management, accounting, legal, evictions, depreciation, landscaping, make ready, utilities in common areas, extermination, insurance, property taxes, building code violation fines, permits, usage fees, security, management, leasing fees, etc.  

I split the gas lines to their individual furnaces in order to bill the tenants directly for their gas usage and I know they pay around $50 for their gas.

The house sits on 0.57 acres, and it can be re-zoned for commercial usage if I bring a commercial buyer to the table.

Yet, being hostile to those who are trying to help you, does seem inappropriate.

Does that imply you're billing your tenants for their individual water usage?  

Is it inappropriate to get copy of tenants' lease?

He cannot afford the water bill due to excess water usage and is barely able to cover the payment plan he has setup with the city.