Cal. Public Utilities Code § 770

The commission may after hearing: (a) Ascertain and fix just and reasonable standards, classifications, regulations, practices, measurements, or service to be furnished, imposed, observed, and followed by all electrical, gas, water, and heat corporations. (b) Ascertain and fix adequate and serviceable standards for the measurement of quantity, quality, pressure, or other condition pertaining to the supply of the product, commodity, or service furnished or rendered by any such public utility. No standard of the commission applicable to any water corporation shall be inconsistent with the regulations and standards of the State Department of Health pursuant to Chapter 4 (commencing with Section 116275) of Part 12 of Division 104 of the Health and Safety Code. (c) Prescribe reasonable regulations for the examination and testing of the product, commodity, or service and for the measurement thereof. (d) Establish reasonable rules, specifications, and standards to secure the accuracy of all meters and appliances for measurements. The commission shall require a public utility that estimates meter readings to so indicate on its billings, and shall require any estimate that is incorrect to be corrected by the next billing period, except that for reasons beyond its control due to weather, or in cases of unusual conditions, corrections for any overestimate or underestimate shall be reflected on the first regularly scheduled bill and based on an actual reading following the period of inaccessibility. (e) Provide for the examination and testing of any and all appliances used for the measurement of any product, commodity, or service of any such public utility.