 Why does Joseph lie about the water supply?
Medical science is unanimous in proclaiming this magic medicine the sole panacea in the entire history of therapeutics." Our condenser broke down, and we've gone without water for five ghastly days." It's bitter as some kinds of sin before it's purified. What's fair is fair, and you have put a different complexion on what seemed at first to be an unconscionable interjection of a middleman between Nature and man's thirst." "On account of the quantity, I'm able to quote a bargain price. Shucks, boys, it hurts me more to charge for water than it does for you to pay. The planetoid man worked the pump while the mayor intently watched the crude level-gauge, crying "Stop!" when it registered the proper amount. "Just the same," Joe griped, "paying for water isn't something you can get used to in ten minutes." In the fragile forest, they soon came across a stream that sprang from the igneous soil and splashed into the small pond whose contents, according to the mayor, was theirs for the asking. They filled their buckets and hauled them to the ship, then returned for more. He uses only one pool, the sweet one! "You don't need any more," said Harvey, dismayed. Johnson's eight-foot son, topped by a massive roof of sun-bleached hair and held up by a foundation that seemed immovable, had obviously been born and raised in low gravity.
 He wants people to believe they need to pay for it.
 There isn't a lot of water there, and he needs to be able to ration it out.  He wants people to believe they need to pay for it.  He wants to keep the fresh water for himself.  He thinks that people would prefer to buy filtered water.