# Reverse Osmosis Water



## Potterychef (Dec 20, 2011)

Hi guys, I am looking to install a new reverse osmosis water system to supplement my rainwater. I will be watering around 1200 square feet. I am looking for any thoughts or advice on the many units available. Any insite would be appreciated. Regards, Doug


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## keithrs (Dec 20, 2011)

I run a kent marine 60 GPD upgraded to 100 GPD.

What ever system you get, I would suggest adding back up to 15% tap back...This will buffer the water so you don't get big PH swings when you add fertilizer or additives. Make sure the tap gos through a KDF or carbon block filter to remove chorine and such.


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## Mike (Dec 20, 2011)

I just purchased a unit for use in my growing area with a capacity of 50 gallons per day. This is more than I need right now with watering and humidification needs and should be adequate for the mid-term (1 to 2 years). I think the questions you need to answer are:
1. How much water do I need on a daily, weekly basis. 
2. Will I be mixing back in tap water or in your case rain water? How much?
3. What will my peak demand be for RO water?
4. Will my use rate increase over time? At what rate?
5. What kind of storage capacity do I have? 20 gal, 100 gal, 500 gal?
6. What frequency will I use the water?
7. Will I pump from a storage tank, or use a pressurized bladder tank?

There are numerous manufacturers out there and even DIY components for you to build your own system. You need to know what your needs are to properly size a system. Sizing for peak demand (all RO water and drought conditions outside) will put you into a larger system than you will need at normal operating conditions, but will provide for your needs throughout the year. If you size for normal operating parameters, you may be at risk during peak demand, but your system cost will be lower. Hope this helps you make some educated decisions.


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## Rick (Dec 20, 2011)

What is the chemistry (Hardness, Alkalinity, conductivity) of your city water Doug?

Better yet if you can get the concentrations of the 7 major ions, we could determine how much you want to shift to RO.

If this is city water, they should be able to supply this info free of charge.


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## Shiva (Dec 20, 2011)

If you can read french, I can send you a text on how to build one cheap.


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## John M (Dec 20, 2011)

....And if you can't read French, you can always cut and paste it into Google translator to convert it to English.

Here's my home made system:






I supply it with very hard, cold, raw well water, which goes through a tiny R.O. booster pump to increase pressure and then down the line to three 75 gallon per day membranes. I stopped using the prefilters years ago. They do nothing now. The raw well water goes through the booster pump and straight to the membranes. This unit runs 24/7 and provides all the water I need except in the summer when it's very hot. At that time of year however, I can draw water from a nearby stream. The membranes never make the full 75 gallons per day; but, I do get about 150 gallons per day in total from all 3.

My system works on a 1:1 ratio of product water to waste water. I accomplish this by kinking the waste water lines just enough to restrict the outflow so that it matches the outflow volume on the product water lines. It's a very crude design; but, very effective.

The booster pump needs to be replaced about once a year, as the raw well water is so hard, they usually just quit after about 12 months use. So, that's a cost of about $150.00 per year. Plus, the membranes last about a year as well. They're $45 each. So, for aproximately, $300.00 a year, I can make all the R.O. water I need for my greenhouse needs.

My greenhouse is 1440 square feet (30' x 48') and it's full! I have 6 benches running the length from the front to the back wall. I thoroughly water one bench each day and mist/spot water the rest of the greenhouse each day. I do not water on very dull days; so, on those days, I get to build up a bit more water in storage. I have a 6,000 gallon cistern underground, next to the greenhouse for storage.

From about September through to the end of April, I have plenty of R.O. available for my needs. Starting in May, I hook up the outdoor water line and begin drawing water from the stream, which I use for watering, not misting. I water the benches in rotation. So, in the summer, when there is lots of light, each bench will be watered on a 6 day cycle. During the summer, I use the stream water to water one bench. Then, I turn a couple valves and switch to using R.O. water from the cistern and I do the spot watering and mist the whole greenhouse with R.O. water, including the bench that was just watered with the stream water. This way, I can use all the water I want without any concern for wasting it or running low, while I'm flooding the pots with the stream water. Then, I thoroughly mist that bench as well as the rest of the greenhouse with the R.O. water. I mist the bench that I just watered with the stream water so that the R.O. can wash off any of the residue that the stream water left behind....so, I have nice, clean, shiny foliage without water marks when it all dries.

EDIT: Notice the waste water lines and the product water lines coming out of the bottom of the membrane housings. The lines were originally from the same roll of plastic tubing. However, over time, the waste water lines have turned dirty grey/black because they are carrying the super high TDS waste water away. The product water lines, which carry the cleaned, purified water, are still clean. This system is about 6 years old now.


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## keithrs (Dec 20, 2011)

Ether way you go, buy one or make one. I would recommend adding a back flush setup to your membrane filter. This will make the filter last up to twice as long.


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## keithrs (Dec 20, 2011)

John M said:


> ....And if you8 can't read French, you can always cut and paste it into Google translator to convert it to English.
> 
> Here's my home made system:
> 
> ...



Quite the setup!


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## John M (Dec 20, 2011)

keithrs said:


> Ether way you go, buy one or make one. I would recommend adding a back flush setup to your membrane filter. This will make the filter last up to twice as long.



Wanting to design the cheapest system possible, instead of adding on a back flush setup, I just monitor the product water output. When it seems to be slowing down, I'll put a cup of Muriatic Acid in each prefilter chamber and set the system running again. The Acid disolves the crude on the membranes and improves product water volume once again without reducing quality. This is done usually at about the 6 month, and 9 month mark, during the life of the membranes. By 12 months when they slow down again, I just replace them.


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## Ray (Dec 20, 2011)

I sell stock and custom-designed RO systems. 

I am building a 200 gpd unit for myself right now that has a 2:1 brineermeate ratio, as opposed to the standard 4:1, so we'll see about the membrane life. I have a well (and no chlorination), so use 20µ/5µ/carbon prefilters. The dual sediment filter setup is new - my current one has a single 5µ sediment filter, but we have a local problem with "iron bacteria" clogging the finer one too fast.


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## keithrs (Dec 20, 2011)

If you need 150 Gal. or more per day I would look at "ultra low energy" RO membranes.... They have a much better ratio.... 1:1 (claimed) and you can get them from 190 to over 2400 GPD on one membrane. You will need to rise the applied pressure up to 100 psi. The cost of the membranes are quite abit more than a standard RO membrane. I just replace my standard 100 GPD RO membrane for $28 and those membrane are $100-300. I will be going to this set up on day!


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## keithrs (Dec 20, 2011)

John M said:


> Wanting to design the cheapest system possible, instead of adding on a back flush setup, I just monitor the product water output. When it seems to be slowing down, I'll put a cup of Muriatic Acid in each prefilter chamber and set the system running again. The Acid disolves the crude on the membranes and improves product water volume once again without reducing quality. This is done usually at about the 6 month, and 9 month mark, during the life of the membranes. By 12 months when they slowing down again, I just replace them.



Interesting!!!! My last filter lasted about 2 years but I only use about 75 GPW. I flush once a month and go off PPM to replace them.....


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## Ray (Dec 20, 2011)

Actually Keith, it's not the membrane that controls the permeate:brine ratio, it's the downstream restriction in the brine side.

The greater the ratio, the longer the life of the membrane. Folks paying for water, and folks living in places where water is a dear commodity often opt to replace membranes more and produce less flush brine. Once certainly could spend more than the cost of a membrane on that flush water in some cases.


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## keithrs (Dec 20, 2011)

Ray said:


> Actually Keith, it's not the membrane that controls the permeate:brine ratio, it's the downstream restriction in the brine side.
> 
> The greater the ratio, the longer the life of the membrane. Folks paying for water, and folks living in places where water is a dear commodity often opt to replace membranes more and produce less flush brine. Once certainly could spend more than the cost of a membrane on that flush water in some cases.



Agreed.... Fouling is just more common when you change the ratio to 2:1 or 1:1. This why flushing regularly is important.

But you can't get more than about 150 GPD on one residential membrane.

Running a ULE membrane will allow you to have the same service life and get 1:1 while getting fair amount of GPD.


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## Ray (Dec 28, 2011)

The simple fact is this: lower the permate:brine ratio, foul the membranes faster - no matter the membrane.

However, sometimes it's worth it.


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## keithrs (Dec 28, 2011)

You can also lower the ratio by putting membranes in stages.... And also by sending the rejected water of X stage(s) through a secondary membrane stage that filters the waste water(commercial) or by sending some of the waste water back through the membrane(s)(residential) 

Rejection % also has a big effect on how fast your membrane will foul. You can almost double your membrane life by going with a 96% rejection vs a 98% membrane. Lets face it... We don't really need almost 0 TDS like reefers... 20-50 TDS will not make much of a difference. If any thing you won't have to add tap water back. I changed my last membrane @ 120 TDS. Alittle high but my water sensitive plants didn't know the difference.

I might add that applied pressure will have an effect on fouling and how much product water you get. Standard PSI for membrane testing is 60 PSI(@ 77deg) to get the GPD. Most houses in the US have about 40 PSI(I have about 35-45 depending on my whole house filter). A simple booster pump will add about 50% more product water per day.


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## Rick (Dec 28, 2011)

Ray said:


> but we have a local problem with "iron bacteria" clogging the finer one too fast.



I hate those bastards!!!!


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## biothanasis (Dec 29, 2011)

Don't RO systems produce waste water? How much is it per litre of RO water produced and what could someone do with it instead of disposing it (so it is practically gone)????


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## Candace (Dec 29, 2011)

biothanasis said:


> Don't RO systems produce waste water? How much is it per litre of RO water produced and what could someone do with it instead of disposing it (so it is practically gone)????




Yes, they produce a lot of waste water and I feel pretty guilty about it as we are metered here. I do make use of it and try to recycle it. I have the waste water tube running to my evaporative cooler. You can also save it to use on lawns and landscape plants etc. It's not recommended to use on any landscape plants that have edible parts or fruit.


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## biothanasis (Dec 29, 2011)

Thank you for the reply Candace.


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## cnycharles (Dec 29, 2011)

some people use 'gray water' to wash laundry, or have a tub so that laundry water is used a few times and then discarded. I guess the flush could be used for laundry somehow unless it was extremely hard


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## Ray (Dec 29, 2011)

A pretty-much-standard RO system produces 4 parts flush water for one part pure. That suggests that the TDS of that flush water will be roughly 25% higher than the incoming supply. Depending upon the starting concentration and what the dissolved solids are, that might not be so much after all, meaning it's perfectly usable for other, less sensitive plants.

If your RO system goes into a pressurized tank (most "plant people" use an open tank, so this doesn't apply), as the tank fills, the back-pressure on the membrane is increased, slowing the production of the pure water, but the flush water keeps flowing so the "waste" ratio increases. That can be overcome by employing a "permeate pump" that uses the flush water flow to draw a slight vacuum on the membrane, so it never sees that back-pressure.

Candace, it is possible to decrease the flushure ratio, but at the cost of replacing the membrane more frequently. If you pay for water or water+sewer, or if you want to be particularly conservative in your water consumption, it's worth it. My new 200gpd system is just a shade over 2:1, and I'm sure I can get it lower, but I'm using it as a test-bed for membrane repacement.

I just did a cost comparison for another forum:

It seems the average cost of water is somewhere between $0.0015 and $0.0020 per gallon in the US (I used the $0.0020 in my calculations). Santa Fe NM was the highest I could find, at $0.0123 for their costliest residential bracket.

Using the most-expensive, standard configuration I sell (5-stage, 100 gpd, 1:4 pure:flush), and using a true output of half that (most get more, depending upon temperature and pressure of the incoming line), adding the municipal water cost drives the price per gallon to $0.034 for the US average, and up to $0.086 for Santa Fe - still a long way from the $1/gallon store price.

If I assume that the sewer cost is equal to the water cost - most are less - those costs/gallon are $0.044 and $0.147, respectively. Still a relative bargain.

I then reran the numbers doubling the rate (and cost) of membrane replacement, and assumed a 1:2 pure:flush ratio (I honestly don't know if they would need to be replaced twice as often with that ratio - the company that sells 1:1 systems recommends replacing membranes annually, so that's what I did here) and the cost comes down for Santa Fe, to $0.105 per gallon RO, while being unchanged for the US average.


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## biothanasis (Dec 31, 2011)

Thanks Charles!!

Very valuable info!! Thanks Ray!!


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## Ray (Jan 1, 2012)

One more thing to consider, besides cost: the use of a pure water source has invariably resulted in reports of better, "brighter" and "cleaner" growth.

We invest a lot to keep our 'chids happy, so maybe this is just one more way.


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## keithrs (Jan 30, 2012)

I wonder if anyone here has use a Nanofiltration membrane for removing hardness.


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## Mike (Jan 30, 2012)

I have considered this as an option. Sizing and flow rates are my biggest concerns, but if you are running this into an open tank, I think you can get pretty good clearance of minerals with these filters. Because they don't pull everything out of the water they tend to give you water between 20 and 50ppm in the product stream. 

I have also looked at the TAC (Template Assisted Crystallization) systems, but I cannot tell with this method if there is accumulation of available minerals and salts. These systems use a media to bind the minerals and flush them out of the pipes without causing the scale problems in hard water systems. I cannot determine if the TAC molecules can be taken up into plant tissues. It would be great if these TACs precipitated and could be filtered out. Has anyone had experience with these TAC systems?


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## keithrs (Jan 31, 2012)

I have not... In fact I have not even heard of this system intel now. From what I have read in a short research study is that TAC media causes certain elements that are in water to bind into crystals "balls" or "seeds". I'm not sure if these crystals seeds are usable to plants with out being broken down by bio life is soil. TAC is a anti-scale media and not a filter. It doesn't remove any thing in the water, only transform it so it can't "stick" to a water pipe ect. That being said.... I'm not sure why you would need this media unless you have scale problems in your water heater or boiler. You may be able to filter the seeds out?!?!?


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