Yes. Harvest rainwater. But it hasn't rained enough in Worcestershire for a month!!!
Now I'll need about two days solid rain to wash the roof properly before I can start collecting it again.
Roll on Winter!!!
And surely saving water is very important. There are TWO ways to save water. The first is to minimize waste when producing it. The second is to minimize usage when washing the windows.
To minimize waste, the approach seems to be to use the highest pressure possible using a booster pump if possible. RO units work most efficiently at the highest pressures.
To minimize usage, use a tap or trigger.
1 - Water on - soak
2 - Water off - scrub
Repeat 1 and 2 until dirt, fingerprints, bird poo etc are removed
3 - Water on - rinse
Soaking and scrubbing at the same time certainly works perfectly well, but I think it uses much more water than is really necessary.