In the beginning of the Green Sky Era, many people fell victim to disease in the water supply. Although the underground system from the pre-creep world still existed and running water was available, it was mostly tainted. In areas near the coast, seawater flooded most of the water tables, rendering huge reservoirs unpotable.
Furthermore, any water pipes that existed on the old grid were more-or-less guaranteed to carry hazardous compounds from the decaying cities. During this time, urban centers and suburbs were pillaged for bottled water; any sort of purified water became a commodity.
Following the years of recovery, water purification technology made leaps forward. Advanced filters were used to tap existing water tables and a gradual return to the old water system came about, though purified rain water remained preferable. The dangers involved in drinking from the old infrastructure decreased yet it was still culturally frowned upon and seen as gross, akin to smoking cigarettes was in the world before.