California Code, Corporations Code - CORP § 14317

(a) The flows set forth in Section 14315 shall be calculated on the basis of a residual pressure of 20 p.s.i.g. in the distribution system under flowing conditions.

(b) Fire hydrants shall be attached to the distribution systems at the locations designated by the entity responsible for their use for firefighting purposes.  Any new mains to which a hydrant may be attached shall not be less than six inches in diameter.

(c) Each separately operated water system shall not have less than two independent sources of supply.