I'm lucky I don't have to worry about osmosis water.
We live in a regional holiday town about 500 metres (1/3 of a mile) from the sea, so no heavy industry to leave pollutants on the roof. We have a 5000 litre (1320 gallons) rain water tank.
I love my water tank, in the eight years we've lived here I've never run out of water, I use it for my orchids and the garden,