How much money can you save replacing an old high-flow toilet with modern low-flow toilets? My house is old enough that we still have toilets that use about 13 liters per flush1 instead of the modern standard of 6 liters or less.
(I bet some readers landed here hoping to catch me using “literally” incorrectly. Maybe they have caught me. I’m literally flushing away something I have to pay for (water), but I’m not literally flushing coins or bills. It’s an important debate to have while I’m somewhere else.)
New dual-flush toilets use either 6 liters or 3.8 liters per flush depending on whether it is a big or small flush. This makes the water savings either 7 liters or 9.2 liters per flush. In my limited experience, low-flow toilets need more second flushes than my old toilets require. Combining this with the fact that small flushes are more frequent, I’ll call the savings an average of 8 liters per flush.
For my 4-person family, I estimate that we flush about 20 times per day on weekends and holidays (116 days per year), and about 12 times per day for the remaining 249 days per year. At 8 liters per flush, the savings add up to 42,464 liters or about 42 cubic meters per year.
With the exciting sewer surcharge of over 100%, I pay $3.25 per cubic meter of water. So my estimated savings on 42 cubic meters is $136.50 per year. Given the uncertainties in the water-saving estimates, we should probably say that the savings are between $100 and $200 per year.
The cost for me to replace 3 toilets is probably about $1000 for the toilets and the inevitable extra parts or replacement of a broken tool. Oh yeah, and I have to include whatever value I place on my labour for this type of work.
Overall, the payback time is in the 7-15 year range. That’s not fast enough to get me excited. I’d have to believe that the cost of water will rise faster than inflation, which seems likely. Another motivator is doing my part to protect our environment. It will take a burst of enthusiasm to overcome my natural laziness on this one.
1 Trying to find out how much water my toilets flush took a little while. They have no convenient markings of liters or gallons per flush. So, I was reduced to the ancient volume trick of length X width X height. The tank length and width were easy (46 cm X 16 cm). I had to actually watch a flush to see how far the water dropped (16 cm). But when the tank hit its low point, the bowl was still filling. So I had to estimate the volume of water to refill part of the bowl (20 cm X 16 cm X 6 cm). Then subtracting an estimate of the volume of stuff (technical term) in the tank, and using 1000 cubic cm per liter gave an estimate of 13 liters per flush. That’ll make you think twice about reading future footnotes.