By Jim Bishop, President & CEO, BEAK International Inc. and
a
long time member of ES&E's Editorial Advisory Board
I was reading about people's attitudes towards drinking water, and came across the following statement: "Many people, when interviewed, say that they would not drink reclaimed sewage water". I was glad I was sitting down when I read that, lest I was bowled over by this revelation. However, it started me thinking about the likelihood that most of us are probably drinking reclaimed sewage water every day, whether we like it or not. This led me to try to prove to myself that we do indeed drink reclaimed sewage water, and to estimate the amount.
First, here's why I think it is likely. One eight ounce glass of water (based on the US ounce, which is 1/16th of a pint), is equivalent to about 240 ml. According to most health authorities, we're supposed to drink eight glasses of water a day. This is corroborated nicely by the value of 1.5 to 2 litres consumed per person per day, the amount used by Health Canada and MOE (sp.) to calculate MACs (Maximum Acceptable Concentration) for various parameters in drinking water.
As a chemist who works with biologists, I know that if we drink that much liquid we will eventually have to get rid of it. To find out how much, I made inquiries to colleagues who have devoted much time to the consumption of liquids, and the best estimate is that we all urinate about 1.5 litres a day. However, some of us are smaller than others, and others are just more dainty or bladder challenged, so I settled on a conservative estimate of one litre of urine per person per day.
What exactly is urine? It is mostly water with a bunch of other things generally referred to as bodily wastes, on which I don't want to dwell. Avogadro (born in 1776, the year of the US' Declaration of Independence) determined that one mole of anything contains 6.02 x 1023 atoms or molecules. Thus, one mole of hydrogen is 1 gram, and one mole of oxygen is 16 grams, so one mole of water is 18 grams, or 18 mL. Also, 18 grams (or mL) of urine, which is mostly water, contains about 6.02 x 1023 molecules of water, so one litre of urine contains 55 times this amount, or 330 x 1023 molecules of water. This means that each one of us passes about 330 x 1023 molecules of water, in the form of urine, each day.
If we could dilute this one litre of urine in all the water on the planet, we would be diluting 330 x 1023 molecules of water that was once someone's urine in 1.4 billion cubic kilometres of water. This is all the water there is: salt water, ice, groundwater, atmospheric water, water in plants, oceans, lakes, rivers, and bottled water. This is 1.4 x 1021 (or 1.4 billion trillion) litres of water. Once the litre of urine was diluted in all this water, every litre of all the water in the world would contain 23,600 molecules of water that was once someone's urine.
Isn't chemistry fun? There are some five billion people on earth, and they all probably urinate about one litre per day. If this was mixed with all the other water, there would be 120 trillion molecules of everyone's urine in every litre of water.
Finally, while this sounds like a lot, if we convert it to a concentration format, it is only 3.6 parts per trillion. There is no Canadian drinking water guideline for urine at present.