wish it were that simple though.
municipal water treatment systems are a lot simpler.
I've done a presentation on the western treatment plant @ werribee 2 semesters ago, constructed wetlands system is a very interesting concept.
/water engineering.
i cant remember the concentrations now, but i think its about 1mg/L of Arsenic allowed
the ground water also has salt that needs to be removed to about 180mg/L.
And there's also magnesium/calcium hardness to contend with.