You really don’t think about it when you flush the toilet, but if you do not have a low flow toilet, you may be using as much as five gallons of water per flush. Multiply that by an average of five flushes a day, and that is a lot of water. In fact, flushing toilets accounts for 38% of water used in a house, and 14% if you also count water use outside the home for watering the lawn, etc.

In 1994, the U.S. mandated that new toilets be low-flow, consuming no more than 1.6 gallons per flush. So if your home was built after 1994, you probably already have low-flow toilets. However, the early models did not perform very well. So read on to understand how they work, in case you need to replace them.

And if your house was built before 1994, you may not have low-flow toilets, and it may make sense for you to consider one as part of a bathroom remodel.

There are basically two types of low-flow toilets. Gravity toilets clear waste by the force of gravity pulling water from the toilet tank into and down the bowl when flushed. Pressure-assisted toilets compress air, which energizes the water that is released into the bowl with each flush. The air is compressed within a vessel inside the tank each time it refills. Pressure flush toilets perform better than gravity flushing units but are a bit more expensive and are noisier than their gravity operated counterparts.

Additionally, there is a third kind of toilet called a high efficiency toilet (HET) which uses even less water – about 1.28 gallons per flush. One type of HET that you might have seen is a dual flush toilet. Push one button, and solid waste is cleared with 1.28 gallons of water. Push the other, and urine is cleared with only 0.8 gallons.

So what do you look for in a low-flow or high efficiency toilet? Here are a few things to consider:

How well the toilet removes waste.
Noise. Noise does not really impact functionality, but can be annoying.
Height. Toilets which are compliant with the Americans with Disabilities Act (ADA), which are about 1.5 inches taller than the average toilet.
Shape. An elongated bowl toilet is easier for men and larger people to use but they stick out 1 to 2 inches further than a round bowl toilet.
Some other points:

If you are looking for a high efficiency toilet, make sure the product is labeled a high efficiency toilet.
Check to see if the toilet has a “WaterSense” label from the Environmental Protection Agency. This signifies that the toilet uses no more than 1.28 gallons per flush and can clear waste efficiently.
There is not a direct correlation between price and efficiency. Price is also determined by aesthetics, such as color and shape.
As you age, also factor in toilet height. As mentioned above, ADA-compliant toilets are higher, and thus are easier for both sitting down and standing up.