then again, anyone with a garden or balcony that has to be watered with a watering can can [sic] attest to how heavy a little bit of water is. If you have a small 100m² garden and it rains a modest 1mm (per m² that is) that's 1L/m² equivalent to 1kg/m² or 100kg total mass of water. When it has rained 1mm people call it "three drops of rain" and they will have to water their plants anyway. That's already 10 cans @ 10L each to lug around.

The other kind of people who know about the weight of waters are people with campers / trailers and people with fish tanks in their apartments. The maximum allowable size for a fish tank in the middle of the room is not that much.