This is a very legitimate complaint to make. A lack of potable water onboard is a health and safety issue, not just an inconvenience issue for a lack of coffee and tea. On a flight like STL-SFO, you can expect a significant number of passengers to use the lavs at least once. The inability to wash hands in the most effective manner - soap and water - becomes a health and safety issue both for that flight itself and future flights until the aircraft receives a significant cleaning.