What is a general assumption when using surface waters for drinking supplies?

When considering surface waters for drinking supplies, a fundamental assumption is that they must be regarded as potentially contaminated. Surface water sources, such as rivers, lakes, and reservoirs, are highly susceptible to pollution from a variety of human activities and natural processes. This includes runoff from agricultural lands, industrial discharges, urban stormwater, and wildlife interactions, all of which can introduce pathogens, chemicals, and other contaminants into the water.

Because of this inherent risk, it is crucial to conduct thorough testing and treatment of surface water before it is deemed safe for drinking. Treatment processes may include filtration, disinfection, and other processes aimed at removing harmful substances. Recognizing that surface waters can be contaminated is essential for ensuring safe drinking water and protecting public health.

The other options suggest specific treatments or chemical additions that are not universally applicable, as not all surface waters require softening, aeration, or fluorides. The need for such treatments depends on the specific characteristics of the water source and the specific contaminants present. Thus, considering surface waters as potentially contaminated establishes a cautious approach before any treatment may be considered necessary.