Carrying water across the desert is a tricky proposition. You need water to live, so you have to carry some. But the more you carry, the more difficult your journey becomes – and thus, the more water you need. Rockets have the same problem; fuel is heavy, so the more fuel you’re carrying, the more you need.
You have to find the right balance between the weight you carry and what that weight gives you.
When you carry other people’s water for them, the calculation changes significantly. That’s a lot of weight to drag across the desert when that weight isn’t giving you any additional ability to do so.
Sometimes there are very good reasons to carry water for other people. But always make sure of two things: One, that the people are worth carrying water for. Two, that it actually is water – and not just rocks.