Before the beginning of each year in which it intends to supply water, a water undertaker must designate the names and areas within its area of supply that are to be its water supply zones for that year.

A water supply zone may not comprise an area whose population immediately before the beginning of the year in question is estimated by the water undertaker to exceed 100,000.

The water quality within a water supply zone must be approximately uniform.

A water undertaker may not vary a designation under paragraph (1) after the beginning of the year in relation to which the designation has effect.