Water testing is a little bit like problem solving. Most people want to know if there are any underlying issues that may affect their water quality. For example if there are higher than expected numbers of bacteria, if there are dissolved metals present or if there is any contamination from organic chemicals. Most test results are ‘indicators’ and go towards characterising water quality. They also give some ideas about both water treatment, for example by using water filters or, often more importantly water supply management.
There are a lot of things that can possibly be in water: algae and microorganisms, organic chemicals, metals, different salts and dissolved gases. But water is not a static system – it is a living (usually) system that has its own properties. One of the most useful tests I do in the lab is to measure carbon dioxide. Specifically its the dissociated fraction that is part of the pH buffer system. By also measuring alkalinity its possible to calculate a theoretical pH. Now when that’s compared to the actual pH some inferences can be made about factors that are affecting water quality. Something similar is done in medicine where analysis of the pH buffer system can indicate if a persons illness is affecting or originating from kidneys or lungs.