Cal. Health & Saf. Code § 40271
Before the first day of September of each year, the bay district board shall estimate and determine the amount of money required by the bay district for its purposes during the fiscal year and shall apportion this amount to the counties included within the bay district, one-half according to the relative assessed value of property on the secured roll of each county, or that portion thereof, within the bay district as determined by the bay district board and one-half in the proportion that the population of each county, or that portion thereof, within the bay district bears to the total population of the bay district.
For the purposes of this section, the bay district board shall base its determination of the population on the latest official information available to it.
The total amount of money required by the bay district to be apportioned to the counties, or that portion thereof, included within the bay district for its purposes shall not exceed two cents ($0.02) on each one hundred dollars ($100) of the assessed value of all the property included within the bay district.
Ca. Health and Saf. Code § 40271