What generally has excellent bacteriological quality?

• A. Ground water
• B. Surface water
• C. Treated wastewater
• D. Seawater

Answer: (A)

Groundwater generally has excellent bacteriological quality because it moves through soil and rock that act as natural barriers. As water filters through the subsurface, many microbes are physically removed or inactivated, and nutrients that microbes need are limited. Adsorption to soil particles and predation by native microorganisms further reduce bacterial numbers, and long residence times in aquifers help ensure fewer viable microbes reach wells. While shallow or contaminated zones can degrade quality, in typical conditions groundwater is less exposed to surface contamination and thus shows higher bacteriological quality than surface water, treated wastewater, or seawater.