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Living Well in the cITy

Toilets and Water Usage

Toilet use accounts for roughly a third of a persons daily water use and it is the largest use of water in your home.

On average, people flush the toilet 5 times per day. The modern toilet: the one you will most likely see in a new home or find available for purchase at home renovation centers in North America, will use 6 liters of water (1.2 gallons) per flush. These are known as Ultra Low Flush (ULF) toilets. Prior to the introduction of ULF toilets in the 1990's, 13 liters (3.5 gallons) flush toilets were typical. These were the "Water Saver" toilets. And prior to that, in the 1980's, toilets were using 20 liters (5.25 gallons) per flush.

In the United States and parts of Canada, all new construction homes must use 6 liter flush toilets. In Australia and Singapore, dual flush toilets are a requirement. I think it is just a matter of time before the same thing happens in North America.



Toilet Technology

Flush Types

A toilet in a hotel room in Zurich Switzerland. Notice the two flush buttons on the wall for selecting small and large flushes

Most residential toilets rely on gravity to get their job done. Water flows out from the tank into the bowl, forcing the water level in the bowl over the trap way. The momentum of the water, thanks to gravity, creates a siphon with the water in the bowl quite literally being pulled up through the trap and down the drain. The bowl is designed to channel the water in such a way as to maximize the flush. This is very important in lower flush models.

Pressure assisted toilets work by using the pressure in the water supply lines to fill a sort of bladder in the tank that is released when the toilet is flushed. The air pressure released from the bladder forces water from the tank into the bowl. This extra push means less water can do more work. These are the sorts of toilets you find in commercial and industrial installations. They can be very loud but work amazingly well.

Dual flush toilets are gravity flush toilets that that offer full and half capacity flushes. For solid waste you would have the toilet use a full flush and for liquid waste, use the lower flush volume. This saves a considerable amount of water. Camora is a company that specializes in toilets such as these.

Tip bucket flush toilets are another less common style that makes use of a bucket in the tank to store the water for the flush. Activating the flush tips the water out of the bucket. This means no flapper in the tank to leak and no sweat on the outside of the tank either.

MaP Rating

MaP stands for Maximum Performance. This is a measure of the amount (weight in grams) of solid waste a given toilet should be able to clear in a single flush. The higher the number, the better the toilet. The range for most residential toilets 350 to 1000g. In the United States, the EPA's WaterSense Program requires a minimum of MaP rating of 350g. If you see the EPA WaterSense sticker on a toilet, it will meet this minimum standard.

How a newer low-flush toilet can save water and money

Reduced Consumption

Obviously, a toilet that uses half the amount of water per flush is going to cut the water usage in your home from flushing toilets in half. But it gets even better if you've installed a dual flush model because out of 5 flushes per day only one or two will be full flushes.

Flush Volume Flushes per day
per person
Use per day
per person
Use per year
per person
Percent saving
over 13 liter
13 liter 5 65 liters 23725 liters ----
6 liter 5 30 liters 10950 liters 54%
dual 3/6 liter 1@6l and 4@3l 18 liters 6570 liters 72%

The 6 liter model alone will cut your consumption in half but notice how the dual flush model cuts that almost in half again. That's because very little water is needed to clear liquid waste from the bowl.

Municipal Rebate

You municipality might offer a rebate on newly installed toilets that meet certain efficiency criteria. In my city, a 6 liter toilet can earn a $60 rebate which is almost half the price of an entry level toilet. Depending on you local building code you might not have much of a choice when installing a new toilet. In Australia for example, a place where water resources are not as abundant as they are here in North America, all toilets must be dual flush models.

Other Reasons To Upgrade

If you are used to an older toilet, you'll be quite surprised at how much more efficient a new toilet is. They don't "run" as long. Newer toilet tanks are typically lined with styrofoam insulation to prevent condensation. And they clear waste very quickly.

I had to have a 20 liter toilet changed in an apartment recently because water was leaking through the floor and into the apartment below. The wax seal beneath the toilet over the flange had cracked with age and needed to be replaced - a common problem in older apartment buildings. Having to lift the toilet from the floor was a good enough excuse to replace it with a 6 liter model.