Beginning in 1994, newly manufactured toilets were limited to using no more than 1.6 gallons per flush (gpf). Before then, flush volumes as high as 3.5 gpf were considered "low‐flow" — and the oldest toilets could use more than 6 gallons! Water concerns in the 70s and 80s led many to try to conserve on their own. One of the more novel ideas was to place a brick (yes, an actual brick) inside the toilet tank: doing so displaces water — about half a gallon — making each flush use less of it.
The idea sounds relatively harmless, but there are risks to consider. It's important to understand that toilets are designed to flush with a specific amount of water; even things that appear to be of little consequence can drastically affect the way a toilet operates. With only water and gravity at work, even an extra inch in the height of the trap or the size and placement of rim holes can play a big role in how well the toilet clears waste. So even if your old toilet looks identical to the newer "low‐flow" model, there could be significant internal differences.
Same model, made in different years. Can you tell the difference?
The waste that goes into your toilet needs to be disposed of properly and completely — it should never end up stuck in the trap or your home's sewer line. The correct amount of water — as determined by the engineers that designed the toilet — is necessary to move waste through the trap and far into the sewage line. Using less water runs the obvious risk of a poor flush, and could even allow sewer gases to creep into the bathroom if there's not enough water left in the toilet trap.
The other primary concern with using a brick is…the brick. Whatever particular materials the brick is made of, it's not meant to be perpetually submerged in water (which is far different than being "exposed to the elements"). There's a good chance the brick will start to break down after a while in the tank, where the loose clay / sand / lime / concrete particles can cause problems in the fill valve and other internal components. Some say to simply wrap the brick in plastic, but this is not reliable protection.
If you want to save water and have an older toilet with a higher flush rate, we strongly recommend that you replace the toilet with a newer, water‐saving model. Stop‐gap measures like water displacement may not present any issues when utilized for a short period, but the only way to safeguard against future problems and annoyances is to have a unit that's designed to save water. If cost is a concern, check with your water provider (or use the WaterSense rebate finder) to see if there's a rebate program in your area: you may be able to get up to $100 to offset the cost of upgrading to a 1.6 gpf model. There might also be local programs that can offer greater assistance to low or fixed income households — make sure to check!
In those cases where you're unable to have a new toilet installed but still insist on saving as much water as possible, there are options. Instead of a brick, try filling a plastic bottle with small rocks or pebbles and screw the cap on — the concerns over using less water (in a toilet designed for more) will still remain, but you'll at least avoid a disintegrating brick. Rubber "bricks" are also available that achieve the same end, without the disintegration risk.
Consider taking the "mellow yellow" approach — forego flushing urine and you can save quite a bit of water each day. Dual‐flush retrofit kits are also available, which allow an older toilet to use less water for flushing liquid waste, or the full flush volume for solid waste — but keep in mind that these will not work with all toilets, and may have an adverse effect on performance (given the lesser volume of water).
And finally, as always: check for and repair leaks immediately! All the conservation measures in the world won't do much if leaks are present in your home's plumbing — be they at the fixtures themselves, or the pipes behind walls.
Want more water‐saving ideas? Check out our Guide to Water‐Saving Plumbing Products for tips to help you conserve!