Inevitably as the weather gets drier those not lucky enough to have a good store of rainwater are wondering how to get hold of clean water.
One possibility we’ve recently been asked about is whether you can use reverse osmosis filters to clean up tapwater.
Reverse osmosis filters – which force tapwater under pressure through a semi-permeable membrane – seem to be sold as domestic appliances for people not happy with their tap water. It looks like they would cost several hundred pounds to get installed, and then have some regular running costs for filters and maintenance.
I haven’t investigated them carefully – just scanned one companies website – but they appear to have a serious flaw as far as ponds are concerned. Although the filters had a very high removal rate for most chemicals – usually in excess of 90% – for nitrate, which will usually be the biggest problem, the removal rate is only 50 – 90%.
So you could fit the filter and then remove only half the nitrate. If your tapwater comes with 25 milligrammes of nitrate in each litre (which it often does) halving this amount would still leave you well above natural levels.
Which brings us to Robert in Lewisham who has a pigeon infested roof with passing traffic depositing all sorts of dirt on the roof as well. And to compound the problem, he has no downpipes to get the water from anyway.
The only practical suggestion I have is to see whether there are any friendly neighbours who might be prepared to share water from their roof. You collect the water from their place and bring it back to your garden pond.
