RO Water vs. Distilled Water

[Cinderella]

What is the difference? I am not planning to get an RO system and I can't collect enough rainwater to use it exclusively.

 

[littlefrog]

The differences are largely in how the water is produced. The end product is pretty similar, probably indistinguishable for purposes of orchid growing. Distillation involves evaporation of water and then condensing the evaporate (which has left the vast majority of impurities behind) into a separate container. Usually this involves the application of considerable amounts of heat (obviously boiling water generates more gaseous water than a room temperature liquid).

RO uses a membrane which is permeable to water, but not to most other things. The impurities get left on one side of the membrane, where they are flushed away and diluted by continuing flow of water across the membrane. This is pretty inefficient, depending on your input water you might get 10 gallons of waste for every gallon of RO water (or 4:1, in a good case). A lot of RO systems now have pumps to increase the input pressure, which increases the efficiency.

That is probably oversimplifying... The practical upshot is that distillation requires lots of energy in the form of heat (some sort of fuel). This can get expensive. Reverse Osmosis spends water instead of heat. If your heat is cheaper than your water, you should invest in distillation. Most places the water is cheaper than fuel, so an efficient RO system is the choice there. I don't really know that one is any harder to maintain than the other. No moving parts in any of those systems (save a pump, maybe). RO systems usually have several fairly inexpensive filters that need to be replaced regularly, and the membrane (more expensive) probably won't last forever. And you will find RO systems offered for sale a lot, I don't know that I've seen many distillation systems for sale. Of course you could make your own still.

 

[NYEric]

I am using about 2 gallons/day to water my orchids and on cleaning days it can run up to 8 gallons. NYC rainwater really isn't an option. At $1.39/gal for distilled water, the R.O. system [and 1 filter change midyear] isn't an expensive tool.

 

[Rick]

Rob
You pretty much hit in on the head, except that the energy/efficiency + capital and operational costs of RO work out not that much better than RO (at least on a large scale). Even on a small scale the operational cost of a coffee maker is probably not that much more than processing the equivalent amount of water through efficient RO.

Membranes are getting better and cheaper, and pumps are getting more energy efficient so the differential is getting more pronounced.

I've heard rumors that pushing water through nano-tubes may be the next wave of water purification:clap:

 

[Eric Muehlbauer]

How much water do you need? You can buy a deionizer sold as a "Tap water purifier" for about $49 from any of the online pet catalogs (Petsolutions, That Fish Place, etc..). Replacement cartridges usually go for around $17. I don't use it for orchids, (NYC tapwater is fine for me....even cyps enjoy it...) but the trace amounts of phosphate make it unusable long term as a top-off for my reef tanks. For me, a cartridge lasts about 4 months. If you're water quality is poor, it won't last all that long. Basically, its worth it if your impurities are minimal. Take care, Eric

 

[Orchidnut57]

Now that I am totally confused...not such a difficult task ...unlike EricNY our gallon of distilled water is only 85 cents but in the yearly total a good bit of money. I have a small collection of less than 100 orchids. Two thirds Paphs/Phrags. I have been told all will thrive with RO but is it really worth the expense when you are an indoor grower? I do have a PUR water filterization kit that I use at present.
Thanks
Jim

 

[Rick]

Jim

I know several growers in the Memphis area that I think are using local tap water with no problems at all. Two are regular contributors on this forum.

In general Memphis gets a lot of its water from artesian wells that is already pretty soft and low in minerals. If it is coming out of the Mississippi I don't think that water is particularly hard either.

I would check with Forrest (Fbrem) and see what he's doing for his collections of orchids and carnivorous plants. You may be fine with just removing the chlorine using a Brita filter, and/or cut the tap water with what ever distilled or rain water you have at the moment.

 

[Ernie]

Yep, for most intents and purposes, the water produced by reverse osmosis, distillation, and deionization are about the same. All drastically reduce the dissolved solids in the water- giving you H2O and little other junk. Each person just needs to decide where they want to spend the money.

*Distilled water requires heat to boil the water (and is a pain in the butt)
*Deionized has a modest startup cost, but requires periodic cartridge replacement and wastes no water
*Reverse osmosis has a higher startup cost and wastes a bit of water (commonly about 4-6 gallons waste water for each gal of keeper water for undersink units)

Brita filters, fridge filters, etc are typically a carbon filter (removes chlorine, colors, odors, but *not* small molecules like phosphorous, calcium, magnesium, etc) sometimes with a particulate filter as well to get rid of sediment.

Softened water is BAD for plants because softeners usually use NaCl as an exchanger. Sodium is bad for plants, and chlorine not so good either. Some softeners substitute other salts which aren't so bad.

If your tap water is decent, you may not need to bother 'fixing' it. For folks that grow in the house, watering properly (deep drenches, not just a top sprinkling) is where I'd focus my attention. If you make/buy "good water" then just apply it gingerly, you're not gaining any ground.

 

[Ernie]

Lots of grocery/big box stores have a pure water dispensor. You simply take your own jug(s) and fill up yourself. The price is commonly about half what pre-bottled water costs. If your Wal-Mart doesn't have a water dispensor, try your local reef aquarium store- they make RO for their own use and many sell it to their customers.

 

[Justin]

i use a small countertop R/O filter that attaches to the kitchen faucet. HIGHLY recommended for a small collection and also inexpensive.

 

[Ernie]

i use a small countertop R/O filter that attaches to the kitchen faucet. HIGHLY recommended for a small collection and also inexpensive.

Hmm, usually the ones that attach to you kitchen faucet (at the faucet end, not under the sink) are carbon and sediment only, not true Reverse Osmosis (like the Pur and Britta faucet filters). But I could be wrong. RO systems usually have a couple "stages" of prefilters before the RO membrane. All these stages would be a bit cumbersome to have on the kitchen countertop.

 

[Orchidnut57]

Ernie you are always on top with the information we ask for. And Rick I have used the artesian water that we are blessed with for over 30 yrs with no bad effects. I spoke with Forrest at our last MOS meeting and he recommended the RO system. For now I use a carbon based PUR filterization system that is attached to my kitchen sink faucet. The filters last 3 or so months and are not too costly. We all wish we lived in Hot Springs, Ar. with their public filler fountains. I have seen folks haul off 'gallons' of the pure stuff. My collection is sitting in 5" tubs with a 1 1/2" deep grid that allows me to water thoroughly without the orchids actually sitting in the remaining water. This also aids in my humidity levels.
Always wanting to improve what I have to create the 'best' for my orchids and I believe Ernie hit it on the nose...if it is working well "do not fix it". Thanks guys . You are the best
Jim

 

[Justin]

Hmm, usually the ones that attach to you kitchen faucet (at the faucet end, not under the sink) are carbon and sediment only, not true Reverse Osmosis (like the Pur and Britta faucet filters). But I could be wrong. RO systems usually have a couple "stages" of prefilters before the RO membrane. All these stages would be a bit cumbersome to have on the kitchen countertop.

Hi Ernie,

I know what you are saying--I was a little unclear in my post.( what, you all can't read my mind?)

The filter unit is attached through tubes, not directly on the faucet itself. There are 3 pre-filters (carbon, sediment) plus the R/O membrane and finally DI resin. It is the same kind of R/O filter you can also install under the sink by tapping directly into the cold water supply. That is the best way to set these up... But since we rent i use a faucet adapter and place the unit on a shelf next to the kitchen counter. Yes, it is a little ugly and it is big but the sacrifices we make for our plants...

I guess the point I was trying to make is these R/O units can be had for fairly cheap and are a great solution for a relatively small orchid collection (I have about 200 plants).

 

[Ernie]

Hi Ernie,

I know what you are saying--I was a little unclear in my post.( what, you all can't read my mind?)

The filter unit is attached through tubes, not directly on the faucet itself. There are 3 pre-filters (carbon, sediment) plus the R/O membrane and finally DI resin. It is the same kind of R/O filter you can also install under the sink by tapping directly into the cold water supply. That is the best way to set these up... But since we rent i use a faucet adapter and place the unit on a shelf next to the kitchen counter. Yes, it is a little ugly and it is big but the sacrifices we make for our plants...

I guess the point I was trying to make is these R/O units can be had for fairly cheap and are a great solution for a relatively small orchid collection (I have about 200 plants).

Ahh, yep. Sounds like A bonafide RO system.

Justin is right in that they aren't as price prohibitive as they used to be. We got a 100 gallon per day (gpd) unit a couple years ago on eBay for about $110 shipped. They do waste water though if you pay for water in/water out.

Note that the rated output is under 'ideal' conditions. Expect a system to give maybe half to three-quarters what it is rated for unless you want to add boosters, temp controllers, etc. We just live with it.