The use and overuse of water is becoming a real concern around the world and you can do your bit.  
For a cheap and easy DIY project in the bathroom, replace your full flush toilet with a low-flow,  this can save as much as 70% of your water usage. Dual-flush cisterns are also great because they control the amount of water being used.  If you don't want to replace the cistern, there are gadgets that fit in the cistern and regulate the float or water level, reducing the flush volume for just a few dollars.  Also, check your water authority as some now offer rebates when water saving measures are used.