Daz I've got a brush with a set on. They definatly save you water. Only thing I found was that it felt really weird cleaning with them as you don't scrub and then rinse separate as you actually rinse whilst scrubbing, if that makes sense, also the noise they make on the glass is really hard to get used to. Other than that they're good and I put mine on if I'm running low on water or if I'm doing a facia/gutter clean.
Daz you not thought of taking some 25ltr barrels out as back up in case you run out? I have a 650 ltr an two of us go through that some days so I carry another 150ltrs around in barrels just in case on certain days