I'm lucky enough to work with a lovely man called Peter who has a lab full of fancy analytical gadgets (mostly bought second hand on Ebay!). One of the things he does is analyse water, so a few weeks ago I asked him to run some home water samples through his gizmos. And here are the results (ppm is parts per million).
|tank no filter||0||5.3||0||0||<1||0||1.2||3.0||0||0.3||0.5||0||6.33||0.00||6.40||28.6|
|scheme + filter||0.9||134||0||0||0||0||16.5||90||0||3.3||5.4||27.4||80.8||0.2||7.7||592|
|scheme no filter||1.1||134||0||0||0||0||16.6||91||0||3.2||5.6||30.0||84.3||0.4||8.0||594|
I took five samples : tank water with no filter (this is the filter we have at our kitchen sink for drinking water); filtered tank water, water scooped from the very top of the tank; filtered scheme water and lastly unfiltered scheme water.
So, what do the results mean? Well the first thing that jumps out is how bad Perth's scheme (mains) water is. The salts (mainly sodium (Na) and Chloride), conductivity, calcium, magnesium, sulphate and bicarbonate are all at least an order of magnitude higher than the tank water. pH is a lot higher in the scheme water too. Perth's water is a mixture of ground water, dam water and desalinated water. The mix changes from suburb to suburb and depending on the time of year and dam levels. These samples were taken in late autumn when dams are pretty low, so the scheme water quality could be worse at this time of year than others. Having said that, Perth's water is relatively good compared to many other parts of Australia and other parts of the world so I shouldn't grumble too much...
The rain water tank was half full at the time and the roof was nice and clean from heavy rainfall so I'm not surprised at how good the tank water is. I tested the top of the tank because I wanted to test whether installing a Waterboy would be beneficial. It's a gadget which takes water from just below the surface of the top of the tank instead of the bottom where it's all mucky, low in oxygen and high in micro-organisms. It appears from these results that it won't help much, although I did take the first two samples at different times to the others due to a problem with some of the samples. Also, I didn't test for the contaminants which the Waterboy claims to avoid, so it probably isn't a fair test.
The other main thing that is striking is that the filter is doing absolutely nothing to reduce any of these parameters. We have an Everpure H54 filter, which removes many things which we didn't test for (eg lead, cysts, dirt and cloudiness, mould and algae. However it claims to reduce chlorine taste and odour and lime and scale build up in things like kettles. Maybe they put taste and odour at the end of chlorine to trick people into thinking that meant chlorine itself, because it definitely doesn't reduce chlorine. And I would assume that lime and scale build up is mainly caused by bicarbonates, which were not reduced significantly in this test. The filter isn't anywhere near the end of its life either, so it's not doing part of its job. That doesn't mean it's doing nothing though and it may be blocking some nasties along the way.
And how does this apply to you? Well, if you don't live in Perth it probably isn't very relevant, especially the scheme water results. However, it does show that if you want good quality drinking water which is low in salts a rain water tank could be a good thing. Rain water still has all the essential minerals your body needs without all the other crap. It doesn't have fluoride which is added to mains water in most western countries to keep our teeth healthy, but if you're worried about that then brush with fluoridated toothepaste. There are many other good reasons to get a rain water tank. Foremost among these is the fact that many water sources are being over extracted to provide cheap water to people. The loser in this equation is the environment of course, which we are actually a part of (easy to forget sometimes) and we depend on for our quality of life. Also, water companies use huge amounts of energy (Watercorp is the biggest energy user in WA) to pump water around and clean it. If you're interested in installing a tank, check out this post for some tips.