Some people say I should put a brick in my toilet tank to save water. How does that save water and is it a good idea?

Toilet flushing uses a lot of water, 40% of a household’s total water usage. Putting something in the toilet tank that takes up space, like a toilet dam or a water filled jug, is a good idea. But putting a brick in the tank is not a good idea. Bricks tend to crumble and might damage your toilet.