Each member of the advisory board shall be appointed for a 3-year term. The terms of the 5 members registered under section 12701 to 12715 shall alternate so that not more than 2 are appointed each year, except that of the first appointees, 1 shall be appointed for 1 year and 2 each shall be appointed for 2 and 3 years. The terms of the members representing the department of natural resources, the water resources commission, and the local health department shall alternate so that only 1 is appointed each year, except that of the first appointees 1 member shall be appointed for 1 year, 1 for 2 years, and 1 for 3 years. Vacancies shall be filled by appointment for the balance of the unexpired terms by the respective officials designated in section 12711.