Sampling Water for Quality Tests You are here: KB Home Water Efficiency Sampling Water for Quality Tests < BackWhy test water?  Many natural waters contain impurities that make them directly harmful to crops. Plants vary in their ability to tolerate and use poor quality water; similarly soils vary in their resistance to the effects of poor quality water. Knowledge of the quality of any given water supply, assessed by chemical analysis, is essential in managing this water in an irrigation system.