Pooping in a flush toilet – it’s one of those magical properties of modern life that is also taken the most for granted.  Once that lever is pressed, the offending material disappears completely from existence.

Of course, it doesn’t really. It goes down the pipes and joins the collective poop deluge we all contribute to each day.  But how large is this deluge being sent to our treatment plants?  No one seems to really know, so I thought I’d try to figure it out.  I went two different routes to find my end number to help make it more meaningful.

For the first method, I worked backwards.  As of March 10, 2016, Calgary’s three water treatment plants were processing 467,426 m³ of water everyday.  That’s over 460 million litres of water, enough to fill approximately 184 Olympic sized swimming pools.

According to a tour guide at one of the Calgary wastewater treatment plants, around 1% of all intake at the plants is solid waste. A lot of that is random stuff flushed down toilets and garburators, which is then caught by “the grit” (a heavy-duty filter system that separates the solids from the liquid.  Find out more about Calgary’s wastewater treatment system).

How much of that is human waste?  We can only guess, so I worked within a range.  I went from a conservative 10% to a generous 50% of solid waste arriving at the plants being folk’s previous meal.  A little elementary math later, it could be from 467,426L to 2,337,130L of poop, every day.  I split the difference and said 1,402,278L.  Unfortunately, this number required too much guesswork to feel meaningful (albeit educated).

So, on to method two.  How does my first calculation compare with how much people poop on average? The average person produces approximately 1 ounce of stool for every 12 lbs of body weight.  According to a Maclean’s article, the average Canadian female weighs 153 lbs, and the average male weighs 187 lbs – for a total average of 170 lbs.   So, a person weighing 170 lbs would produce just about .88lbs of poop a day (or 14.16oz).  But not everybody in Calgary is an adult! 28.8% are 18 or younger – average weight of around 80 lbs producing an average of .41 lbs of poop a day.

Per a density conversion website, 1 litre of poop weighs around around .88lbs.  Therefore, the average volume of poop produced a day by the average Canadian would be around a litre for adults, and about half a litre for kids.  With a population of 1,235,171 in our fair city, around 30% being kids, there would be around 1,045,179L of poop flowing to our water treatment plants every day – which falls in the lower end of the range of 10% to 50% of solid waste being feces established before (it would be around 20%).

Conclusion: we’re either flushing a lot of solids that aren’t poop into our sewers, or we poop at above average rates.  My instinct tells me the latter, as this is Alberta where we like to do things bigger.

I split the difference between the two and called it my answer: 1,223,728.5L of poop collectively weighing around 1,076,881 lbs. Roughly.