This is actually an interesting point... that perhaps that tank was cut off from supplying water for a certain period of time. Then, someone turned it back on and that is when there were indications that something very bad was going on that affected the water. Because all of the other true cases (meaning not movies) of people being in water tanks it seems the poor quality of water was detected much sooner. I believe in one the people consuming the water noticed that it was VERY bad within 24 hours. Granted, this was in a warmer climate than L.A. in winter and the tank may have been smaller.. but 18-19 days is a long time. Now, I do not know why or how the tank would be cut off, however that makes a certain amount of sense. Although I do think some people exaggerated about the water because AT's water was clear. I hate to talk about the water when Elisa's life is more important. But, I have honestly wondered why she wasn't found sooner just because of the water.