Flow cytometry (FCM) can now be officially used for the quantification of microbial cells in drinking water. The new analytical method - developed at Eawag and extensively tested both in Switzerland and abroad - has been incorporated into the Swiss Food Compendium (SLMB) by the Federal Office of Public Health (FOPH).

FCM provides much more realistic results than the conventional method, in which bacterial colonies are grown on agar plates. The results demonstrate that even good-quality drinking water harbors 100 to 10,000 times more living cells than the conventional plate count method would suggest. 

http://www.news-medical.net/news/20130125/Flow-cytometry-can-now-be-used-for-quantification-of-microbial-cells-in-drinking-water.aspx