The effect of sediment on water quality

ESR scientist Dr Chris Nokes discusses the effect sediment can have on microorganisms in the water. It is possible that microorganisms survive longer in sediment than they do in water, and when it rains, this sediment is stirred up and the water becomes difficult to treat.

Transcript

DR CHRIS NOKES The work that we have been doing on microorganisms and sediment is to understand how long organisms will survive in sediment. If bacteria or viruses survive longer in sediment than they do in the water, then sampling the water may be giving us an incorrect indication of the level of contaminants that may be present in that whole environment. One of the things that have become apparent from disease outbreaks that have occurred in first world countries is rain events, or changes in conditions in the source water, can have quite an impact on the risk to a water supply. The problem that a water treatment operator faces is, if they are taking water from a river, rain events increase the flow of water into the river, therefore the river flow increases, and as a result of that, sediment is stirred up in the river. So they have a very hard time during rain events, primarily for two reasons. One is that they have a lot more mud and sand and things that they need to get rid of from the water, so they are having to change the way in which they treat the water. At the same time, the numbers of potential disease-causing organisms may increase in the water as well. So not only are they having trouble controlling the treatment process, but the levels of contaminants are also increasing.

Acknowledgements TVNZ TELEVISION ARCHIVES Watercare Services Ltd