Question:
I have been watering my plants with distilled water (instead of tap water)for several months now, and I'm very happy with this solution. However, asthe waterings become more frequent (approaching summer), and as mycollection continues to grow, buying gallons and gallons of distilled waterevery week is becoming more and more inconvenient.So I'm considering buying a reverse-osmosis unit.Ideally, the one I'm looking for one1) is very small: I don't think I'll ever need more than a couple ofgallons/day, and I would like something that I can install under the kitchensink;2) is of good quality: I would like to keep my orchids as happy as they arenow.I'm pretty much clueless on the subject, so I have the following questionsthat I hope someone of you might be able to answer:a) What are the main differences/advantages/disadvantages betweenreverse-osmosis and distilled water (I hope not to start a holy war here)?b) Do you have any advice on what/where to buy?c) Are you using one of such units? What are your experiences with it?

Answer: I've never dealt with a reverse-osmosis unit, so I can't help you there,but I would like to (as usual) add a picky warning (I feel like the towncrier whenever I post).

Out in the research greenhouses on campus here (one of which is full oforchids) we water using deionized water (not from bottles but from a DIline). We have to add calcium back into the water (something which is notfound in most, if any, fertilizers). Relevent to the earlier thread onmineral removal using epsom salts, we have a separate fertilizer tank forthe orchid food and another for calcium sulfate because if you keep thetwo together the calcium precipitates out.

The reason I mention this is because the symptom for calcium deficiency isnecrotic lesions (actually, a total calcium deficiency will result in aslimy mass that used to be a plant) - the reason is that calcium is neededto stabilize cell membranes and cell walls (those of you who make fruitpreserves think pectin, which happens to be a cell wall component).Calcium normally isn't added to water lines because it's normallyplentiful in both soils and tap water. Many of the organic mixes peopleuse (mud mixes, bark to some extent, etc.) probably have enough calciumto retard the occurance of lesions, but it's always a good thing to watchfor if you are using purified water of some sort (deionized, distilled, Idon't know the extent to which RO removes calcium).

Incidentally, the reason Davis uses DI water is twofold: 1) we do researchand some people like to control what's in their water, and 2) Davis waterhas toxic levels of some chemicals (boron, for example).