Cal. Wat. Code § 20205
If a petition protesting against the adoption of the ordinance is presented to the governing board of the water district prior to the effective date of the ordinance, the ordinance shall be suspended and the governing board shall reconsider the ordinance.
If the number of votes cast for all candidates for Governor at the last gubernatorial election within the boundaries of the water district exceeds 500,000, the ordinance is subject to referendum upon presentation of a petition bearing signatures of at least 5 percent of the entire vote cast within the boundaries of the water district for all candidates for Governor at the last gubernatorial election. If the number of votes cast for all candidates for Governor at the last gubernatorial election within the boundaries of the water district is less than 500,000, the ordinance is subject to referendum upon presentation of a petition bearing signatures of at least 10 percent of the entire vote cast within the boundaries of the water district for all candidates for Governor at the last gubernatorial election.
Ca. Water Code § 20205