Reverse Osmosis Systems

[aerides]

Originally Posted by Ray

...A standard residential system is a 4:1 system; 4 gallons of incoming water will produce 1 gallon of pure, with the three remaining gallons used to flush the rejected dissolved solids away. Folks use the flush water for less sensitive plants, let it spill on the greenhouse floor for humidity, or as I did, to refill a pond for the local fauna in my neighborhood.

There are 3:1 and 2:1 systems available, but I recommend going no lower than the former, as the membrane can foul too quickly.

Thank you for your great support, Ray. One question for now just for clarity, and later a call would be great. Will PM you when I feel prepared for that. Oh, the question for now is, when you said recommend going no lower than the "former", did you mean no lower than the 4:1 you mentioned in the former paragraph, or the 3:1 system you mentioned first in the paragraph that contained the recommendation? Thanks again. --John

---------- Post added at 09:22 AM ---------- Previous post was at 09:18 AM ----------

Originally Posted by Ray

A standard residential system is a 4:1 system; 4 gallons of incoming water will produce 1 gallon of pure, with the three remaining gallons used to flush the rejected dissolved solids away. Folks use the flush water for less sensitive plants, let it spill on the greenhouse floor for humidity, or as I did, to refill a pond for the local fauna in my neighborhood.

There are 3:1 and 2:1 systems available, but I recommend going no lower than the former, as the membrane can foul too quickly.

Thank you for your great support, Ray. One question for now just for clarity, and later a call would be great. Will PM you when I feel prepared for that. Oh, the question for now is, when you said recommend going no lower than the "former", did you mean no lower than the 4:1 you mentioned in the former paragraph, or the 3:1 system you mentioned first in the paragraph that contained the quote? Thanks again. --John

---------- Post added at 09:25 AM ---------- Previous post was at 09:22 AM ----------

Apologies for the double-post. I didn't see the first one (not realizing that the thread had gone to page 2. Oops. Great thread by the way. Thanks so much everyone!

---------- Post added at 09:47 AM ---------- Previous post was at 09:25 AM ----------

Originally Posted by mook1178

I have extensive knowledge in aquaria. RO vs DI is still a big debate in that field. Is it still a debate in horticulture. I'm part of the DI camp and there are 2 main reasons why. RO systems to get pure water still require DI cartridges on the back end. No 2 is that RO systems waste more water than they make. Environmently with water shortages happening all over the world,I think DI is a better choice.

Thank you, mook 1178. Looking into this option.

[Roberta]

A big part of the RO vs DI debate is economic... I priced out both, given the amount of water that I planned on needing for the orchids, and DI would have been prohibitive for me. Orchids don't need water to be as pure as an aquarium system so DI not needed. (RO removes most of the TDS but not all, for orchids 20 ppm TDS is quite adequate) With RO, it is important to remember that there IS waste that is still good water for other purposes, and factor that into your plans.

[mook1178]

Originally Posted by Roberta

A big part of the RO vs DI debate is economic... I priced out both, given the amount of water that I planned on needing for the orchids, and DI would have been prohibitive for me. Orchids don't need water to be as pure as an aquarium system so DI not needed. (RO removes most of the TDS but not all, for orchids 20 ppm TDS is quite adequate) With RO, it is important to remember that there IS waste that is still good water for other purposes, and factor that into your plans.

Thank you Roberta. That makes sense. I used to have a fairly inexpensive di system. It was around $50 when I bought it close to 10 years ago. I have not been able to find it online now though. Economics then made sense to use di over RO.

Are orchids really that sensitive to tap water? Obviously the chlorine is bad, but that can be removed with carbon or even just letting the water sit overnight with a pump to move the water.

[aerides]

Originally Posted by mook1178

Thank you Roberta. That makes sense. I used to have a fairly inexpensive di system. It was around $50 when I bought it close to 10 years ago. I have not been able to find it online now though. Economics then made sense to use di over RO.

Are orchids really that sensitive to tap water? Obviously the chlorine is bad, but that can be removed with carbon or even just letting the water sit overnight with a pump to move the water.

It depends on the tap water. Chlorinated water (my understanding) can be allowed to sit and the chlorine will dissipate. My NYC tap water seemed fine for general purposes, but some paphs seemed to object to it. (At the time, I told them to get over it.) My tap water here in the NJ highlands comes out of the ground. I need a standard house water softener to protect my pipes from scaling, etc. But even though "they say" that there is such a little bit of sodium added through the softening process, I have absolutely noticed that it affected phal roots badly - and phals aren't particularly notorious for being sensitive. I've been using purchased spring water and that seems fine (should take a TDS reading). But even so, it's expensive and inconvenient to water orchids with purchased water. Thus the RO/DI "research project."

[Ray]

Aerides - I meant 3:1 (3 gallons raw water in = 1 gallon pure water out), which is the same as the Hydrologic "2:1", meaning 2 flush plus one pure.

A typical residential RO system will remove roughly 98-99% of the dissolved solids. There are also low-pressure membranes available, and they still remove 92-93%. If a grower has really hard water and adds a softener for household use, then an RO system is great, as Na and Cl are much more easily removed than the calcium-, magnesium-, and iron carbonates that usually cause the "hardness".

Mook - As Roberta pointed out, the demands for aquaria are far beyond those of orchids, so DI is unnecessary. Straight tap-to-DI is doable, but costly, as the ion exchange resins need to be recharged or replaced periodically, and that can be costly.

If you really dislike water wastage and have no good use for the flush water, there are a couple of alternatives, but with a price:

One is to use an even smaller flow restrictor on the flush water outlet, which brings the ratio of pure to flush down to about 1:1, but that's going to reduce the typical membrane life from about 12,000 gallons down to 5,000-6,000. They cost around $45 to replace.

Another is to convert your system to a "zero-waste" type by purchasing a pumping system that takes that water and "injects" it into the household hot water supply. Cost is about $200.

[mook1178]

You guys rock!

Aerides-you are correct that chlorine will dissipate. Having a pump in the water for movement will speed that process up. I'm a chemical oceanographer that has a lot of experience with this.

Ray-I like your suggestions of the injection into the hot water system. When I had my reef tank, man do I miss it, it was small enough that tap to DI was reasonable and the system I had I could make 5 gallons in about 15 min. I used to do 15 gallon water changes weekly on my tank. It worked out great for my use. The cartridges were only about $30 and would last a couple months, but I also ran the water through 2 cartridges. I did that so that all resin in the first cartridge was used up. In DI systems, this is extremely important. As the cartridges get used, the resin in the middle is used faster than the resin on the outside, creating a false sense of filtering. The second cartridge would take care of that.

We do not need a softener for our water. Is there something specific in city tap water that is bad for orchids, ie flourine? I can see the sodium causing a problem from a softener tank. The Na is what helps to soften the water. It creates a chemical matrix similar to salt water, nowhere near has high of a concentration though, that will help to precipitate metals from the water.

[Roberta]

If the water is safe to drink, I don't think that there is anything in it that would be toxic at any level. It is mostly a matter of solids (salts) and pH. If the solids include a lot of sodium chloride (like from seawater intrusion) it will be an issue at a lower level than "hard water" - calcium carbonate. But most orchids in nature live on rain water, which is very low in minerals (but not zero!) Some are fussier than others. (I have found Catts, Cymbidiums, Phals don't care... and they get tap water) Paphs actually like the minerals (The Huntington Botanical Garden uses well water 200-800 ppm TDS on their world-class Paph collection) but Phrags and Pleurothallids really want that RO water. If water is high in calcium carbonate, the pH also stays stubbornly at 7.8 - 8.2, and is not moderated significantly by fertilizer. Ideal orchid pH is around 6 - 6.5 for most, much easier to achieve with the low amount of minerals of RO water (which is naturally neutral, around pH 7)

[mook1178]

Originally Posted by Roberta

If the water is safe to drink, I don't think that there is anything in it that would be toxic at any level. It is mostly a matter of solids (salts) and pH. If the solids include a lot of sodium chloride (like from seawater intrusion) it will be an issue at a lower level than "hard water" - calcium carbonate. But most orchids in nature live on rain water, which is very low in minerals (but not zero!) Some are fussier than others. (I have found Catts, Cymbidiums, Phals don't care... and they get tap water) Paphs actually like the minerals (The Huntington Botanical Garden uses well water 200-800 ppm TDS on their world-class Paph collection) but Phrags and Pleurothallids really want that RO water. If water is high in calcium carbonate, the pH also stays stubbornly at 7.8 - 8.2, and is not moderated significantly by fertilizer. Ideal orchid pH is around 6 - 6.5 for most, much easier to achieve with the low amount of minerals of RO water (which is naturally neutral, around pH 7)

Absolutely correct with the CaCO3. the pH of the ocean is buffered by carbonate and bicarbonate, keeping it at a pH of ~7.9. This is a strong buffering system, so water with CaCO3 will have the same buffering, but not to the extent of seawater. Fertilizers do not have acids in them, for the most part. The P in the fertilizer may even turn to phosphate, depending on the water used, which is another buffering chemical that will keep the pH high.


This has been a nice distraction this morning from trying to wrestle data from my instruments that were lost in the Gulf of Mexico for a few months.

[Ray]

Most municipal water authorities use chloramines nowadays, and it does not dissipate readily. I have heard that it is bad for your plants, but I've been using our tap water with it for about two years, and nobody is complaining.

Aerides- If you're in NYC, you probably don't even need to consider RO! You've got one of the purest municipal water supplies in the country. (Sorry I missed that in your earlier post.). At most I'd get a big carbon filter to remove unwanted organics.

[aerides]

Originally Posted by Ray

If a grower has really hard water and adds a softener for household use, then an RO system is great, as Na and Cl are much more easily removed than the calcium-, magnesium-, and iron carbonates that usually cause the "hardness".

Ray, just confirming. I do have a typical softener system. So I absolutely would want to RO post-softened water? Makes sense, and great that the softener can do some of the work. I don't think I'd be able to repurpose the waste, which at my projected needs may not be "criminal." Especially if the three-stage model would be okay. Maybe a tank someday to store for outdoor garden water. Also, as long as I'm planning, I may want to get into pleurothallids. the highly sensitive D. cuthbertsonii and the like some day. Would hope that the water from a 3:1 system would work for these as well(?) Thanks again.

---------- Post added at 12:35 PM ---------- Previous post was at 12:33 PM ----------

Originally Posted by Ray

Aerides- If you're in NYC, you probably don't even need to consider RO! You've got one of the purest municipal water supplies in the country. (Sorry I missed that in your earlier post.). At most I'd get a big carbon filter to remove unwanted organics.

No, we're good. I live in New Jersey highlands now. New York was an "earlier life."