Water purification tablets dont work on kegs? [SDL 0.9-814-gde9bdf9]

In my current version of cataclysm [SDL 0.9-814-gde9bdf9] I have run across something that might be considered a bug and a balance issue with regard to water purification tablets.

I have an aluminum keg with 101 charges of water, and a pack of 42 water purification tablets. When i try to use the tablets on the keg (held in hand) it says that i dont have enough charges. However it only takes one tablet to purify a gallon jug of water (15 charges of water.) By this math i have enough purification tablets to purify 630 units of water.

This is probably a case of the purification tablets taking the entire jug size into account when trying to purify it, instead of the actual volume of the liquid.

For balance purposes, just how many charges of water should purification tablets work on anyway? I would estimate that a single tablet should purify 1-3 units of water?