Nearly one million Californians use contaminated water to drink, shower, and cook, but the state’s politicians want to change that—including by amending the constitution or taxing certain products.

Two state assembly members, Republican Devon Mathis and Democrat Eduardo Garcia, filed language Jan. 16 to amend the state constitution to require that 2 percent of the general fund budget be set aside each year for water quality, supply, and delivery projects in the thirsty state.

Passage of the...