If you don’t have a low flow toilet, use plastic bottles filled with water and pebbles
to replace water in the tank. Don’t obstruct the float and don’t use a brick.  Standard
toilets can use as much as seven gallons of water per flush. Low-flows? A mere
16 gallons. If you want the water savings of a low-flow toilet, but aren’t
ready to shell out for a new toilet, you’re in luck. With a few simple
modifications, you can turn your water-guzzling toilet into a water-sipping
low-flow just by using some simple household items. You can even purchase a
tank bag, fill it with water and hand it in your toilet tank, this will also
reduce the amount of water needed to refill the tank after each flush.