Cal. Civ. Code § 37.111.111

(1) An establishment using a nonpublic water supply system must have water samples analyzed for coliform bacteria as follows:
(a) Coliform sampling must be done before licensing and in at least two different months of each calendar year that the establishment operates.
(b) The sampling schedule must include collection when the water source is most likely to be contaminated, such as during April through June and September through October, in the high ground water season, or as directed by the local regulatory authority.
(c) The local regulatory authority may require the establishment to sample monthly, in the months the establishment operates, or if an inspection, sampling results, or an event indicates the water source is vulnerable to contamination.
(d) The local regulatory authority may return the sampling frequency to two in a calendar year if an on-site sanitary inspection of the water source and other pertinent information shows the water source is no longer vulnerable to contamination.
(2) Following shock disinfection, a coliform sample must be collected at least three to five days after disinfectant is no longer detected in the system.
(3) An establishment using a nonpublic water supply system must have a water sample analyzed for total nitrate before initial licensing and at least every three years that the establishment is licensed.
(4) Water samples must be analyzed by a laboratory licensed and certified by the state of Montana for drinking water analysis.
(5) The establishment must ensure water test results are transmitted to the local regulatory authority from the laboratory in a format acceptable to the local regulatory authority within five working days, except as required in ARM 37.111.112 (1)(c) and (3)(d).
(6) The establishment must keep test results available for inspection by the local regulatory authority for at least five years.