Small-System Water Treatment Operations for Class S
Start with the source, because it determines everything else
Ground water that is properly protected has been filtered by soil and rock, so it often needs
only disinfection. Its characteristic problems are dissolved iron and manganese, hydrogen
sulfide, hardness, nitrate and sometimes naturally occurring contaminants - and
protection of the wellhead and the aquifer, since the barrier is natural and invisible.
Surface water carries turbidity, organic matter, seasonal swings and the pathogens of a
surface source - including Giardia and Cryptosporidium cysts, which chlorine does not reliably
inactivate at practical doses. That is why surface sources require filtration as well as
disinfection, and why filtration performance is monitored so closely.
**Ground water under the direct influence of surface wat