a way to prevent unsafe water from entering the drinkable water supply is to

A way to prevent unsafe water from entering the drinkable water supply is to install backflow prevention devices such as vacuum breakers, air gaps, pressure vacuum breakers, and double check valve assemblies. These devices prevent contamination by stopping the backward flow of unsafe water into the clean water supply. In addition, physical measures such as placing grates over drains and keeping grease traps clean help maintain water safety. Furthermore, holistic water safety involves multiple barriers including preventing hazards from entering the source water, removing particles and contaminants through treatment, killing pathogens, and maintaining water quality during distribution. Proper inspection, maintenance, and structural measures like raising well heads, screening water sources, and restricting access to contamination sources also play a crucial role in protecting drinking water. Thus, installing backflow prevention devices combined with systematic source protection and treatment barriers effectively prevents unsafe water from contaminating drinkable water supplies.