To begin with, please consider the best business practices when billing water/sewer to MHP residents:
1) Does your state utility commission /county/city allow billing tenants for sub-metered utilities. Most specifically allow under one of the jurisdictions; others are "quite" allowing utility sub-meter billing by default. In some states you'll need to file with the jurisdiction prior to billing your tenants.
2) In most cases an owner/manager/sub-metering service can not make a profit on the utilities: tenants are billed at the same rates and typically the same rate structure as the municipal supplier. A reasonable billing fee is allowed if using a third party billing service.
3) Meters should be kept in good working order. (Replace your old meters)
4)Tenants should have a means to reconcile the utility charges on their individual sub-metering bill.
That said, estimating usage charges or applying arbitrary flat charges for your tenants' "utilities" are not a good idea. If you can't accurately bill the tenants for their water/sewer use; you're probably better off just increasing the rent.
The recent extensive legal actions by tenants in Ohio concerning sub-metering and overcharges, should be considered when billing tenants for any utility.
We’re here to answer your water sub-metering questions.
Southern Water Management