California Code, Civil Code - CIV § 1954.212

(a) If a monthly submeter reading necessary to measure volumetric usage is unavailable, and the tenant has provided access to the submeter, the tenant may be charged 75 percent of the average amount billed for volumetric usage for the last three months for which complete billing information is available.  The adjustment shall be disclosed on the bill.

(b) If no complete billing information is available for the prior three months, the volumetric usage charge shall be deemed to be fifty cents ($0.50) per day that the data is not available.

(c) If monthly submeter readings remain unavailable for more than six months, the volumetric usage charge shall be deemed to be zero for any subsequent month that the data is not available.