Cal. Civ. Code § 37.111.112

(1) If coliform bacteria is detected in a nonpublic water supply routine sample, the establishment must:
(a) collect at least four more repeat samples within 24 hours of notice at the following system points:
(i) the location of the original contaminated routine sample;
(ii) up-gradient to the contaminated routine sample;
(iii) down-gradient to the contaminated routine sample; and
(iv) at the source; or
(v) as directed by the local regulatory authority.
(b) collect at least five routine samples in the month following a detection of coliform in any routine sample; and
(c) notify the local regulatory authority within 48 hours of receiving each test result.
(2) If coliform is detected in a repeat sample, the establishment must:
(a) take appropriate corrective action; and
(b) notify customers and staff by placing an advisory sign approved by the local regulatory authority at each point of use, or as directed by the local regulatory authority.
(3) If fecal coliform or E. coli is detected in a routine sample or repeat sample, the establishment must:
(a) stop using the water source immediately;
(b) provide a temporary source of safe water in accordance with ARM 37.111.114 ;
(c) take appropriate corrective action; and
(d) notify the local regulatory authority within 24 hours of receiving test results.
(4) If an establishment fails to take the four repeat samples or the five routine samples, following the detection of coliform, or the laboratory fails to test for fecal coliform or E. coli in coliform positive samples, the establishment must follow corrective actions as specified in (3).