This water widget works best in Firefox. With I.E., however, it works functionally, but due to quirks in I.E.'s colspan tag, which I have been unable to work around, some of the text alignment goes awry, thus it looks prettier in Firefox.
This calculator is fairly complicated as far as calculators go. You may wish to read the accompanying notes before getting stuck in. The notes can be found here. The note numbers in the right-hand column (green) will take you directly to the relavent note.