Expert: George Maxwell - 10/11/2007

Question
QUESTION: Are there any dangerous chemicals in basic house tap water? If so what are
they?

ANSWER: Thanks for your question.

The answer depends on two things:

1) What's "dangerous"? Water itself is fairly hazardous depending on the situation: you can drown in it, it reacts explosively with hot fats, alkali metals etc...  Obvoiusly, you're interested in the toxic materials that may be found in water, but it's an important point: all substances have hazards and benefits, so be careful about applying loose defiitions like "Dangerous substances".

2) Where do you live? All tap water has to pass basic tests for levels of common inorganic and organic toxins, and so should be safe to drink.

Water's a great solvent, and so most sources (man-processed or not) contain dissolved substances such as toxic heavy metals and their compounds, as well as fluorides, chlorine salts (from water chlorination), and numerous other salts. In most developed nations, a careful check is kept on the levels of these compounds, to ensure they aren't present in amounts likey to cause problems for human heath.

Whilst a sufficent quantity of any of these materials wouldn't do you any good, the small amounts present in drinking water are unlikely to have any adverse effect. Take chlorine: in concentrated form, it's a deadly gas that has been used as a chemical warfare agent, but in small quantities,it kills harmful bacteria in the water supply, eliminating killer diseases like cholera.

Your location plays a big part in determining what material is present in your tap-water, and there have been cases of severe contamination of local supplies. An English village, for instance, suffered from the effects of aluminium poisoning when too much of an aluminium-based water treatment chemical was released in to the supply.

Overall: water is so good at dissolving things that most sources will contain a variety of dissolved compounds: what these are, and the amounts present, will depend on your locality. Usually, the amounts of chemicals that are considered hazardous to human health are kept to a minimum by careful and regular inspection and analysis by local government and water companies.

---------- FOLLOW-UP ----------

QUESTION: Like, other than urnaium and lead, but like other natural or human made poisons that get into our tap water

Answer
Thanks for the follow-up.

Uranium and Lead are examples of  "heavy metals" that I mentioned earlier in my first answer - so-called because they have dense nuclei.

As I said, location is the key: for example the water in London is unlikely to have heavy levels of Uranium in it, but water from Cornwall (which has higher levels of naturally radioactive rock in the ground) may contain measurable quantities.

Similarly, Lead isn't found in most main supplies, but some houses still have lead internal pipes, and so the amounts of lead are likely to be higher in those houses.

"Natural poisons" are likely to be bacteriologcally based, and again this depends on where you are and on the local conditions. Have you noticed that after a storm, water from the tap often tastes more strongly of chlorine than usual? That's because the risk of bacteriological contamination increases with more floodwater enterng the treatment plant, so the levels of chlorine put in to deal with this contamination is increased.

Basically, your question is difficult to answer because "drinking water" is different depending on where you are. Small quantities of most common compounds will be found in all water supplies, but the exact amount, and whether they pose a hazard to health depends on the location.

Perhaps the best answer is that you need to make an intelligent guess as to the sources of contamination likely to affect your local supply, e.g. if you live in a farming community, maybe there might be pesticide contaamination; if you live near a lead or tin mine, there may be heavy metal contamination etc. Your local water board will provide you with details of the tests that their water undergoes before it's piped to you.