Some work recently out of my former institute, Eawag, has been optimizing a novel method, flow cytometry, to measure microbes swimming/floating in water. A couple of fluorescent DNA dyes are added to the water, then as a very narrow capillary stream flows by a laser, the cell numbers are counted. Initial results have shown that there are a lot more microbial cells in water supplies than we might like to think. Ambient water in the environment (e.g., a lake) generally has maybe 10^7 cells per milliliter (i.e., 10,000,000 cells per drop of water). A soil or sediment has 1-2 orders of magnitude more cells per milliliter in general. The flow cytometry results show that treated drinking water has roughly 10^5 cells per milliliter (i.e., 100,000 cells per drop of water). That’s a lot of microbes in your water! Time to freak out, set your hair on fire, and switch to bottled water! The government is trying to kill you!!
Ok, it’s not that bad. When water leaves a drinking water treatment plant, it is usually given a healthy dose of chlorine (“chlorine residual”) to keep microbial growth low in the piping network to your house. Furthermore, there are tests for potentially dangerous bacteria, with standards to be met before the water is allowed to be delivered to you. A common problem with standard tests is that they require the cells to grow on agar plates, even though many cells don’t grow under those conditions, and the results take up to 3 days. Flow cytometry is available just minutes after sample collection. The Eawag method has revealed that the standard test is a little misleading — no “bad” microbes doesn’t mean no microbes at all, and that’s ok.
What’s interesting is that the Swiss authorities have added this method to the list of acceptable tests for drinking water quality. Who knows, maybe you’ll soon see this method coming to a water treatment plant near you!
Oh, and if you were going to switch to bottled water, just remember, it might have more microbes in it than tap water. It will be ok.