There are many good reasons to get a composting toilet. Water conservation is definitely one of them.
But let’s consider if this water conservation will also save you money.
How much water does a composting toilet use?
Most composting toilets are waterless. They use no water. Some composting toilets do use minimal amounts of water, but for the sake of argument we’ll be comparing a waterless composting toilet to a regular flush toilet.
So the answer is: zero gallons per year
How much water does a regular flush toilet use?
In the United States, the 1995 National Energy Policy Act mandated that all new toilets use no more than 1.6 gallons of water per flush. Not all toilets are new, however, and the U.S. Geological Survey estimates that the average toilet uses three gallons per flush. That’s the number we’ll go with.
According to the American Water Works Association, the average American toilet is flushed five times per day.
One year is 365 days.
3 * 5 * 365 = 5475
So the answer is: 5475 gallons per year
What’s the cost of 5475 gallons of water?
In 2013, Slate quoted the American Water Works Association’s finding that the average price of tap water was $0.004 per gallon.
0.004 * 5475 = 21.9
So the answer is: $21.9
5475 gallons of water is a lot of water.
$21.9 is not a lot of money.
Considering that composting toilets cost $1000 or more, it would take you at least 45 years (and about 246,375 gallons of water!) to make back your investment based on the savings from reduced water usage.
So the answer is: While here are many good reasons to get a composting toilet, and water conservation is definitely one of them, this water conservation won’t save you much money.