Not all of us live in a city where you can get spring water directly from the tap. Playing on our fears of water pollution cover-ups, the Sharper Image offers a $10 device that measures if your H2O is pure. In addition to checking the tap, you could also use it to see if that bottled or filtered water you are paying for is really worth the extra price.
The Water Checker measures water for the Total Dissolved Solids (TDS) in parts per million (ppm). The device is powered by 2 AAA batteries and, as Cool-Gadgets aptly quips, is by necessity waterproof.
Jan Schlichtmann and Erin Brockovich would be proud.