The numbers in the episode are:
- 2.5 million JPs of water per week for the whole fleet.
- One third of the fleet relied on Galactica for water recycling, so about 0.8 million JPs needed each week, or roughly 0.1 million JPs per day.
- 10 million JPs lost in the explosion.
- Nearly 17 million JPs of water on Galatica, with "close to 100% effective" recycling.
- 7 million JPs leave Galactica 6 days supply, but when supplying the others only 2 days.
This isn't enough information to figure out exactly what the situation was, but numbers can be found that fit, for example (these aren't the only ones possible, but they do to demonstrate):
- Assume that the water lost by the ships that can't recycle well is negligible (i.e. they manage to get most of it to Galactica as waste water that she can recycle).
- Galatica needs 25% of the 0.1 million JPs per day (i.e. a disproportionately large amount given the population, because it's a battleship, and knowing this the makers built good recycling).
- It takes 5 days on average to do a waste water recycle (i.e. convert the waste into useable water).
- 6.5 million JPs are needed to recycle up to 1 million JPs of waste water (this water is used in the process, but at the end you're left with all the water clean, including the 6.5 million). The unknown recycling process could very well require a large supply of nearly-100%-clean water.
Before the explosion, we see that there's no danger of hitting the minimum level required (after several years the small amount lost to the not-quite-100% process and supporting the other ships would drop the level down to dangerous levels).
After the explosion, supporting the other ships, we see we're dead after 2 days, because we cannot recycle. (There's a month of water left, but no way to get more cleaned, and they were having a lot of difficulty finding new sources at this point).
After the explosion, not supporting the other ships, we see we're dead after 6 days.