I'm a little more invested in house maintenance than a renter typically might be. When I saw our water usage go up, I asked for and received permission to install low-flush toilets and take the bill off the rent.
When I measured the space, though, I realized that I couldn't fit a new toilet into the existing wall space; the darn thing was set too close to the wall to accomodate a new tank. So I bought a piston-plunger flush valve, to retrofit the existing tank. It turns out that it's the water pressure that does the job, not water volume. So the piston works by opening the tank valve super wide, and using the bottom-most volume of water (which is at the highest pressure) and then closing rapidly and holding on to as much as 8 inches of water up in the tank.
This first, most indescribably tedious task, was to remove the tank. The nuts had rusted completely solid to the bolts. However, the bolts still had plenty of good hard steel to them. I had to use a hack-saw blade, slipped between the tank and the bowl, to cut through. Boring, boring, and potentially bloody. I had to hold the blade just tight enough to slide across the bolt but not my flesh, while not so tight that I dug the teeth into me. Yech. Bah.
Finally though, I did get the tank off. I installed the piston, put everything back together with some new hardware, and went from using about 8 gallons per flush to using less than 3!
Pretty cool, eh?
I got my waterbill... I saved $2.73 and so the moral is: conserve water because you want to, not because it'll put more money in your bank.