It all depends on how many plants you have. I live in a flat and don't have a huge lot of plants, some on the windowsill, and some in a Nepenthes tank.
I have used a distiller for a number of years now when I can't get rainwater. I just run off a gallon in about four hours when I need one, simple, no mess and no waste water. It looks like a mini dalek when you put tapwater in and distilled water comes out of a spout.
You can Google distiller and see what you get. Mine is an Ecowater distiller, which is an American brand. I got mine from the Holistic Research Centre who used to be near Cambridge but I believe that they are somewhere in Hertfordshire these days, again try Google.
If you need a lot of distilled water, the downside is they can use a lot of electricity. It should be possible to run off three gallons per day which would be enough for a six by ten foot greenhouse to get by on. They are far cheaper, however than buying deionised water commercially. Mine works out about 15 p per gallon, half that if you are on Economy seven.
I have had my distiller for a number of years and mine was £130 new. I understand that they are quite a bit more than that now. To a degree, you get what you pay for.
This conversation does come up on the forum from time to time. Carl (Mobile) always like deionising filter systems and for some reason doesn't like distillers. The downside with deionising systems is that they need to be used otherwise it buggers the filter. They are also very wasteful of water, you get five gallons of waste water for every one gallon of deionised water.
It all depends how much water you need.
Edited by David Ahrens, 28 July 2012 - 00:59 AM.