Tex. Water Code § 13.503

(a) The utility commission shall encourage submetering of individual rental or dwelling units by master meter operators or building owners to enhance the conservation of water resources.

(b) Notwithstanding any other law, the utility commission shall adopt rules and standards under which an owner, operator, or manager of an apartment house, manufactured home rental community, or multiple use facility that is not individually metered for water for each rental or dwelling unit may install submetering equipment for each individual rental or dwelling unit for the purpose of fairly allocating the cost of each individual rental or dwelling unit's water consumption, including wastewater charges based on water consumption. In addition to other appropriate safeguards for the tenant, the rules shall require that, except as provided by this section, an apartment house owner, manufactured home rental community owner, multiple use facility owner, or condominium manager may not impose on the tenant any extra charges, over and above the cost per gallon and any other applicable taxes and surcharges that are charged by the retail public utility to the owner or manager, and that the rental unit or apartment house owner or manager shall maintain adequate records regarding submetering and make the records available for inspection by the tenant during reasonable business hours. The rules shall allow an owner or manager to charge a tenant a fee for late payment of a submetered water bill if the amount of the fee does not exceed five percent of the bill paid late. All submetering equipment is subject to the rules and standards established by the utility commission for accuracy, testing, and record keeping of meters installed by utilities and to the meter-testing requirements of Section 13.140.

(c) Except as provided by Subsection (c-1), in addition to the charges permitted under Subsection (b), the rules shall authorize the owner or manager of a manufactured home rental community or apartment house to impose a service charge of not more than nine percent of the costs related to submetering allocated to each submetered rental or dwelling unit.

(c-1) The rules may not authorize the owner or manager of an apartment house to impose a service charge under Subsection (c) on a resident who:

(1) resides in a unit of an apartment house that has received an allocation of low income housing tax credits under Subchapter DD, Chapter 2306, Government Code; or

(2) receives tenant-based voucher assistance under Section 8, United States Housing Act of 1937 (42 U.S.C. Section 1437f).

(d) For purposes of Subsection (c), "costs related to submetering" means water costs as well as any other applicable taxes and surcharges that are charged by the retail public utility to the owner or manager of a manufactured home rental community or apartment house.

(e) The utility commission may authorize a building owner to use submetering equipment that relies on integrated radio based meter reading systems and remote registration in a building plumbing system using submeters that comply with nationally recognized plumbing standards and are as accurate as utility water meters in single application conditions.

(f) This section does not limit the authority of an owner, operator, or manager of an apartment house, manufactured home rental community, or multiple use facility to charge, bill for, or collect rent, an assessment, an administrative fee, a fee relating to the upkeep or management of chilled water, boiler, heating, ventilation, air conditioning, or other building system, or any other amount that is unrelated to utility costs.