Reverse Osmosis For Make Up Water

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M

MCT

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Jun 20, 2015
13
South Lyon, MI
Our make up water source is a well that contains iron, which I beleive is the source of some iron staining. I am planning on treating the existing iron stains with the ascorbic acid procedure and then sequestering the iron using an agent for the remainder of the season. After opening next year, the plan would be to drain and refill the pool with fresh water. So as not to have the iron stains reappear and continue to have to use a sequestering agent, I was entertaining adding a reverse osmosis system to the make up source. I have found residential (Pentair) units that can produce approximately 15 gals/day and light commercial units (Oceanic Water Systems) that claim to be able to produce 100, 150, 200 and 300 gallons per day.

Has anyone tried this setup? If so what RO system did you use and what has your experience been?
 
Even residential units will produce more than you might expect when you aren't putting the output into a pressure tank. I have one that I got for watering our plants that processes at least 100 gallons a week pretty easily. I put the output into a 55 gallon drum with a float switch to control the RO unit. Our well water is loaded with sodium carbonate, and will kill many plants. I imagine you could do something similar.
 
Just remember that at low pressures RO is not as efficient. You also have to consider how much loss the system will produce in terms of waste water. Low pressure RO systems typically have low recovery ratios. Also, if the iron content is high enough, membrane fouling can be an issue and would require a definite maintenance cycle to keep the system operating efficiently.

Just some thoughts. It would be neat to see the setup if/when you install it.


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Having maintained a large reef tank I used RO exclusively. If you DO try it, I'd advise getting an inline TDS meter both before, and after the RO filter so you can see when the membrane needs replacing.

You'll also possibly need a booster pump to make it more efficient, but will still lose a lot of waste water. You will likely waste at LEAST 3 gallons for every gallon of purified water. You can let it go down the drain, or collect it for other purposes.

It worked great for daily top-off of a 300 gallon tank, maybe 500 gallons in the system total, as well as water changes but I can't see it keeping up with a pool myself unless you have a lot of patience for a fill, as well as some kind of storage tank for topping it off. It should work though, other than the waste and the time waiting for it to produce water.
 
MCT, I'm not sure you'd really get the capacity you need from a residential R/O without constantly fouling the membrane.

Even if you cover your pool at night, average evaporation at a quarter in a day would be 1 -2" a week, which in your pool should be roughly 600 - 1200 gallons makeup water per week. If your auto cover means significantly less loss, then I could be all wet ;)

I am on well, in Michigan (nights colder, pool warmer= more evaporation) and have both an R/O and dual tank water softener.

The R/O is only used for occasional drinking water in a studio attached to house, and it is constantly iron fouled.

Some weeks (we keep our pool at a therapeutic 88-90 and do not cover due to footprint) I can use 800-1200 gallons makeup water in a week if there's no rain.

I have a soft-water spigot plumbed outdoors to use for makeup water. That reduces the iron to a much lower level...I'm down to around .3 ppm this year.

Alternately, you could look into an Iron Curtain, but if you have it tied to your whole house, again you'd just want to watch capacity and regeneration.

Whatever route you go, you'll want to keep an eye on your calcium levels since you're gunnite...and could conceivably need to add calcium after a while if your makeup water is soft ;)

That is true whether you choose R/O or soft water.

PS Are you keeping your ph low, eg 7.2 to help prevent staining? That helps, as does proteams Metal Magic at higher amounts will in my pool reduce stains as well.
 
NeedMoreSun said:
Having maintained a large reef tank I used RO exclusively. If you DO try it, I'd advise getting an inline TDS meter both before, and after the RO filter so you can see when the membrane needs replacing.

You'll also possibly need a booster pump to make it more efficient, but will still lose a lot of waste water. You will likely waste at LEAST 3 gallons for every gallon of purified water. You can let it go down the drain, or collect it for other purposes.

It worked great for daily top-off of a 300 gallon tank, maybe 500 gallons in the system total, as well as water changes but I can't see it keeping up with a pool myself unless you have a lot of patience for a fill, as well as some kind of storage tank for topping it off. It should work though, other than the waste and the time waiting for it to produce water.
Click to expand...


Hi NeedMoreSun,
Thanks for the information. Can you tell me the manufacture of your RO system and in line TDS meters?
 
Swampwoman said:
MCT, I'm not sure you'd really get the capacity you need from a residential R/O without constantly fouling the membrane.

Even if you cover your pool at night, average evaporation at a quarter in a day would be 1 -2" a week, which in your pool should be roughly 600 - 1200 gallons makeup water per week. If your auto cover means significantly less loss, then I could be all wet ;)

I am on well, in Michigan (nights colder, pool warmer= more evaporation) and have both an R/O and dual tank water softener.

The R/O is only used for occasional drinking water in a studio attached to house, and it is constantly iron fouled.

Some weeks (we keep our pool at a therapeutic 88-90 and do not cover due to footprint) I can use 800-1200 gallons makeup water in a week if there's no rain.

I have a soft-water spigot plumbed outdoors to use for makeup water. That reduces the iron to a much lower level...I'm down to around .3 ppm this year.

Alternately, you could look into an Iron Curtain, but if you have it tied to your whole house, again you'd just want to watch capacity and regeneration.

Whatever route you go, you'll want to keep an eye on your calcium levels since you're gunnite...and could conceivably need to add calcium after a while if your makeup water is soft ;)

That is true whether you choose R/O or soft water.

PS Are you keeping your ph low, eg 7.2 to help prevent staining? That helps, as does proteams Metal Magic at higher amounts will in my pool reduce stains as well.
Click to expand...


I keep the pool covered most of the time. I shut off my autofill so I can monitor losses. I don't think I have ever seen more than 1" loss in a week. We have a whole house water softerner, and RO systems at three sources of drinking water. I just beleive that the softner isn't removing all the iron, or is autofilling the pool while the softner is regenerating. Regarding pH, we keep the pH at 7.5 for swimming comfort. I would rather eliminate the iron then lower our pH and be a slave to sequestering agents.
 
In most home construction, the plumbing is designed such that the spigots are on separate runs from the main and do not run through the main house loop. This is typically the case because you don't want to irrigate with softened water (it's drives up the softener usage for no good reason).

I don't know your plumbing situation, but if your auto fill is hooked up to an outdoor spigot line, then it may not be getting softened water at all.


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Mine was made by Water General, but replacement membranes run about $60 not counting the sediment filters and carbon block. For the amount you would need they likely won't last long. I also just found on their website that input water should be less than 1ppm dissolved iron and to use a water softener before the RO to extend life. As someone above commented just that helped them a lot and it may be cheaper to get a whole house size one of those even if dedicated for the pool.
 
Mct, joyful is correct -- unless you specifically have softened water plumbed to the outdoors, your norml exterior lines wil be well water. Did the PB plumb the auto fill to a softened interior line?

What kind of ppms are you dealing with in the raw well water?

At one inch a week, you'd still be needing close to 600 gallons in your size of pool.
My well runs about 2 ppm iron and our RO membrane fouls fast...likely due to Need More Sun's observation ;)

If your iron ppm is high, eg 2, the softener will not completely nail it and you may get trace amounts...I get about .3 ppm still sometimes. A dual tank helps on the regeneration front as one regenerates while the other supplies.

If you do decide to go with RO, keep us posted. Lots of us would be interested in how that works out ;) Getting off te "Magic" habit is a personal fantasy of mine!
 
Swampwoman, having used RO/DI for many years raising my coral, one thing I learned was the "waste" water was still more pure than the input supply. Nothing I'd want to add to my reef tank, but hated it going down the drain. It was in an entire room full of tank equipment and there was no convenient way to use it though.

Out of curiousity and if you get a chance, besides comparing the iron on the input and the purified side see how much iron is left in your waste discharge. If worried ONLY about iron instead of TDS that waste "may" be just as good. In my tank I looked only for TDS as near zero as possible but was an entirely different need.
 
NeedMoreSun said:
Swampwoman, having used RO/DI for many years raising my coral, one thing I learned was the "waste" water was still more pure than the input supply. Nothing I'd want to add to my reef tank, but hated it going down the drain. It was in an entire room full of tank equipment and there was no convenient way to use it though.

Out of curiousity and if you get a chance, besides comparing the iron on the input and the purified side see how much iron is left in your waste discharge. If worried ONLY about iron instead of TDS that waste "may" be just as good. In my tank I looked only for TDS as near zero as possible but was an entirely different need.
Click to expand...

I don't see how the waste water could be lower in impurities than the output water. It will be higher because all of the solute is in the waste stream but only part of the water.
 
Swampwoman said:
Mct, joyful is correct -- unless you specifically have softened water plumbed to the outdoors, your norml exterior lines wil be well water. Did the PB plumb the auto fill to a softened interior line?

What kind of ppms are you dealing with in the raw well water?
Click to expand...


Yes the autofill is tied to the soft water. Along with the pool, we added a 1200 SqFt pool house and 300 SqFt equipment room. So all the new construction is fed with soft water.

I don't know my pre or post water softner iron content (yet). I'm looking for an iron test kit, but the Taylor K-1716 high limit is 2ppm, I'm not sure that's high enough for the pre softener water.
 
MCT, my understanding is that if your raw water iron ppms are above 2, something like the iron curtain I linked earlier is ideal...if less than 2 ppm, generally the softener should handle it provided your auto fill isn't catching it during regeneration. So in theory, a back up softener tank might work if under 2 ppm raw, or an iron curtain if over, or maybe a higher capacity RO for either if you soften the water first ;)
 
Swampwoman said:
MCT, my understanding is that if your raw water iron ppms are above 2, something like the iron curtain I linked earlier is ideal...if less than 2 ppm, generally the softener should handle it provided your auto fill isn't catching it during regeneration. So in theory, a back up softener tank might work if under 2 ppm raw, or an iron curtain if over, or maybe a higher capacity RO for either if you soften the water first ;)
Click to expand...


So my water is less than 1.5ppm both pre and post softener. What I don't know is the breakdown between ferric (treatable with filter) or ferrous (treatable with softener). I have a water "specialist" coming out Tuesday to review the situation. Without seeing the staining yet he isn't ruling out the source as MANGANESE. I will say that he is pretty familiar with the water breakdown in our area, as he been in business since 1977.
 

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