The discussion yesterday about the presence of hydrogen sulfide in Paula P's well water compelled me to write a short treatise on drinking water. It's pretty boring...but what would life be without borings to a soil scientist? You may want to just scroll down to some hotlinks I've provided near the end of numerical standards for drinking water contaminants. These hotlinks will provide a resource for which you can compare your own water analysis to.
In nature, there is no such thing as absolutely pure water. All drinking water, whether from ground water or surface water sources contain some impurities. The presence of impurities does not necessarily mean the water is unfit or unsafe for consumption. For instance, the majority of water I drink is impure...I do this by choice...most of my consumption of water is in the form of coffee, soda, milk and...and....well, barley pop. Some would say that all of these liquids are polluted water. (Indy drinks that fancy-shmancy French spring water in her mansion...Perrier....it is also "impure" water.)
Most of us get our water from wells (i.e, ground water). When precipitation enters the soil and percolates through it, it dissolves numerous materials...mostly minerals and salts, and some soluble organic compounds from humus. When you think of it, soil and bedrock is nothing but minerals and metals....it only makes since that some of these minerals would end up in the ground water we drink.
A good example of dissolved minerals was the water test results that Caroline shared a few weeks back. Her well water had significant levels of the dissolved minerals calcium and magnesium in it....likely due to the limestone her well is finished in. Paula P's well water, on the other hand, has significant levels of hydrogen sulfide (H2S). H2S is not a dissolved mineral, it is a dissolved gas....it smells like rotten eggs (the kind Indy has on her countertop) However, as I believe Kevin explained, H2S is formed by natural processes of bacteria that live in the groundwater.
Chances are the water Paula P. has moved thru a mineral called gypsum, which is calcium sulfate. Consequently, sulfate (SO4) would be dissolved by this precolating water. Now, all bacteria need a source of oxygen to metabolize....the natural bacteria in Paula's ground water , which are called "sulfate-reducers," use the oxygen in the dissolved SO4 as their oxygen source. In other words, the bacteria "inhale" SO4 and then "exhale" hydrogen sulfide (I know my old soil micro prof is turning in his grave with that analogy!).
No amount of "shocking" a well is going to stop this biological process from happening....well, it may stop it close to the well temporarily, but her well is receiving water from the entire aquifer. (Besides, some people think that water high in H2S is perty nifty. I can remember going to a hot springs spa once...I think it was near Banff, Alberta. I walked into that place and thought I had just walked into a SEWER! The smell of H2S gas was so high it almost made me gag....but the hot mineral water and steam bath was terrific, not to mention Ingrid the masseuse...but I digress.)
So one may be wondering how can I be assured that my well water is safe to drink. Well, people here have suggested that you have your well water tested...this is a good idea. The problem is, most well water testing programs, like those from county health departments, only test for nitrates and the presence of fecal coliform. Yep, just two of out 100's of potential contaminants. Now some others may conclude, okay so I'll have my well water tested for all contaminants...well that's an idea IF you have several thousands of dollars to spend on analyses. As a reference, I've included some links below to state and federal drinking water standards. This will give you an idea of the magnitude of potential contaminants in drinking water. (Note that calcium, magnesium or H2S are not in any of the lists)
Health Risk Limits for Groundwater
National Primary and Secondary Drinking Water Standards
So what is the answer? Have your well water analyzed for the standard nitrate and fecal coliform tests....99.999% of the time, if a well is contaminated it will be due to one of these parameters. Then talk to extension, health departments, neighbors, well drillers, etc. about other potential sources of contaminants in the vicinity...find out what these are, if any, and then perhaps decide to have your well water analyzed for those specific contaminants. You'll save a lot of $$$$ by doing it this way versus the "shotgun" approach of having every possible contaminate tested for. And remember, it is highly unlikely that you'll ever get test results for well water that are all zeros....numbers greater than zero do not necessarily mean the water is unfit for drinking. Compare the numbers to those provided in the hotlinks above.
--Happy Trails, CF
