[citation][nom]IfItsYellowLetItMellow[/nom]For a couple bucks, any toilet can modified with a simple kit. I installed 2 of them. On the rubber stopper, it can be adjusted from level 1 to 9. Higher number being the standard amount of water used when it is flushed. I have all mine set to 4. This means a full toilet could be flushed several times per tankful. If its yellow, flush and release. If its brown, hold it down (to allow more water for flushing). Im pretty sure its less than ten bucks.[/citation]
Here's a method that has been used for years and is totally free.
Put a brick in the bottom of the water cistern of the toilet, reduces the total volume of water in it, doesn't require a plumber to visit, is easily removed or can be increased with additional bricks.
But seriously, this is the kind of thing that can really change the world, have a faster PC or a 3D TV isn't going to save lives or get a Nobel peace prize, I reckon Bill is gunning for a call.