Choosing an RO system?

[FatDragon]

My wife wants an RO system for clean drinking and cooking water. I want to use it for brewing water that I'll start treating to style. I can find systems on sale for as little as $70 and up to the low thousands. I should note that we're in China so suggesting a particular system from a US retailer isn't going to cut it for us.

So, with that in mind, what are the basic things we need to understand about choosing an RO system, other than cost and filter life? What do the various filters do? What about flow rate and efficiency? Systems with a tank versus systems that go directly to a faucet? Waste water? In short, what do I need to know to make an informed decision on an RO system for household and brewing use?

 

[mongoose33]

I don't know if there are any that go directly to a faucet--I believe those systems are pushing RO water through the faucet from a tank.

Here are some things I've learned about RO systems (I have one I bought from Buckeye Hydro):

1. If you think you're going to use a lot of water, get a higher flow-rate unit. I bought one that nominally should do 50 gallons per day, but the price of a 100-gallon unit was only about $7 more, and i wish I'd bought that. I'm only brewing w/ that water, nothing else, but I'd like the capability of refilling faster.

2. If your water is softened already, the system is more efficient and the filter will last longer.

3. On mine, the output is a slow dribble. I have softened water so mine is probably doing about as good as it can, and I get in the area of 1.5-2.0 gallons per hour.

4. Pressure matters. I'm running mine at about 50psi. If your local pressure is low, you'd probably want a higher capacity system, everything else being equal.

5. Home systems run the RO water into a tank that feeds the sink faucet (a separate faucet). Tank sizes are a few gallons. If all you want/need RO water for is drinking or cooking, then a few gallon size is probably fine. Most/all have a shutoff valve so when the tank is full, off it goes.

6. There is significant wastewater. You'll run probably 3-5 times as much water through the system as you get RO water out.

I've attached a pic showing my application; since I'm using it for brewing water only the exact configuration probably isn't right for you, but it may give you an idea that works in your context.

I'm running mine off a hose-thread on the faucet. Note the output goes right into the Aquatainer where I store most of my RO water. I enlarged the makeup air hole in the Aquatainer to 1/4" which means the output tube fits perfectly.

If you don't need a lot, maybe something like that would work. One advantage of such a setup is it can be easily moved to another place. In the pic below, the white tube is the RO water output; the blue tube is the supply from the faucet (covered by a red rag); the yellow tube is the wastewater.

 

[mabrungard]

A system similar to what Mongoose shows, should be sufficient. That is a 3 stage system with carbon and sediment pre-filters. Be aware that the membrane is what sets the system output. In addition, recognize that water viscosity is a BIG factor in membrane production. Cold water does severely reduce throughput. If you are in a cold-weather region, supplying your RO system with heated water is not a bad idea. I soften only my hot water supply, so taking heated water from that circuit helps with production and reduces the effective wasting rate.

Running your RO into a float-valve equipped vessel would allow you to more safely step away from the system while collecting water. If you need to supply your household, you need a big pressure tank to provide enough capacity to avoid frequent running out. I have a 20 gal tank and I can supply up to about 10 gal before the tank runs out (this is normal for pressure tanks).

 

[FatDragon]

A system similar to what Mongoose shows, should be sufficient. That is a 3 stage system with carbon and sediment pre-filters. Be aware that the membrane is what sets the system output. In addition, recognize that water viscosity is a BIG factor in membrane production. Cold water does severely reduce throughput. If you are in a cold-weather region, supplying your RO system with heated water is not a bad idea. I soften only my hot water supply, so taking heated water from that circuit helps with production and reduces the effective wasting rate.

Running your RO into a float-valve equipped vessel would allow you to more safely step away from the system while collecting water. If you need to supply your household, you need a big pressure tank to provide enough capacity to avoid frequent running out. I have a 20 gal tank and I can supply up to about 10 gal before the tank runs out (this is normal for pressure tanks).

Some questions for you or anyone else who can help:

1 - What's the point of systems with 4-7 stages as compared to a 2-3 stage system? We're in a region (heck, a continent) where tap water is not considered safe to drink without boiling and/or filtration. Does that change the outlook of how many stages (and what particular filters) we should be looking at?

2 - Were does the waste water go? Is there a wastewater tube that routes it down the drain or wherever else we want it to go? Is it suitable for other uses like watering plants, washing dishes, or filling a fish tank?

3 - For systems that come with a tank: is the tank typically equipped with a float valve or do I have to actively control the filling of the tank? Can I replace the tank myself at home or is the tank inextricably built in to the system?

 

[ajdelange]

In a full up system you will have
1)A water softener
2)Coarse particulate filter
3)Fine particulate filter
4)Carbon filter
4a)Pressure gauges for determining pressure across pre filters
5)Pressurization pump
5a)Pressure gauge
6)RO membrane
7)Adjustable concentrate restricter valve
8)Feedback valve
9)Conductivity/TDS meter
10)Flow meters (permeate, concentrate, feedback)
11)Polish filter
12)Atmospheric tank with float switches
12a)Pump to fill pressure tank
13)Pressure tank with pressure switches

A basic 'under sink' system will consist of items 3, 4, 6 and 13 with possibly 10. Recovery on those systems is very low (typically 20% or less) so they can be used with fairly hard water. They operate on line pressure so throughput is also quite low - a liter per hour or so. To increase throughput one adds a pressure pump. To increase recovery (to 50% or even a bit more) one adds item 7. To increase recovery even further, at the expense of rejection) one diverts a portion of the brine back to the input of the system for a second pass through it (item 8).

Item 1 is to remove calcium and magnesium to the point that even if their concentrations are trebled or quadrupled in a system with high recovery they stay below the saturation concentrations which would precipitate calcium carbonate or magnesium carbonate or other salts. This is an important aspect of high recovery systems operation. Recovery must be kept below the level which will precipitate the "limiting salt" i.e. the one most likely to precipitate on and foul the membrane.

Item 2 removes large particles

Item 3 smaller ones

Item 4 is there to remove chlorine, chloramine, and organics. Chlorine and chloramine shorten membrane life.

Item(s) 4a measure the pressure drop across the pre filters. Increasing pressure across the filters indicates that they are clogging and need to be replaced.

Item 5 raises the pressure across the membrane thus forcing more water through in a given time period.

Item 7 allows adjustment of the rate of outflow of concentrate and thus the pressure the pump can maintain across the membrane and hence the throughput and recovery.

Item 8 would only be found in whole house or industrial systems where it is necessary to maximize recovery (minimize waaste water production). It controls the amount of concentrate fed back to the pump input.

Item 9 allows monitoring of system feed and permeate ion contents which is an approximate measure of overall rejection.

Item(s) 10 allow the operator to adjust the output and feedback valves for desired recovery (which can be over 70%).

Item 11 removes any organics which have made it through the membrane.

Item 12 serves as a reservoir of RO water e.g. the HLT or as a holding tank from which a pressure tank is supplied. The float switches shut off the feed and RO pump when the atmospheric tank is full. Where an atmospheric tank is used the pressure across the membrane is maximized and thus so is throughput.

Item 12a transfers water from the atmospheric tank to the pressure tank at the desired pressure tank pressure level.

Item 13 stores water at pressure which makes it convenient to dispense be it through a sink top bib or more elaborate plumbing (which must not be or metal as RO water is quite corrosive). If there is no atmospheric tank the pressure tank is connected directly to the membrane permeate line in which case the tank is pressurized from the feed through the membrane. This simplifies control as when the pressure tank is at the same pressure (minus the osmotic pressure) as the feed no more water flows through the membrane. But as this level is approached throughput clearly drops.

With all these filters bacteria would probably be blocked but would viruses, cryptosporidium cysts ...? I personally probably would not want to rely on them alone.

Brine disposal: It indeed goes wherever you pipe it but where you pipe it depends on how much more concentrated it is than the feed. In an under sink system it is only 20% or so more concentrated and you could use it for pretty much anything you use the feed water for. In a high recovery system it is, however, as much as 5 times more concentrated and you would need to think about whether such a brine would be suitable for watering plants, for example.

A system with a pressure tank (but no atmospheric tank) is, as noted above, self regulating with respect to the permeate level in it. Most modern systems are equipped with a pressure operated feed valve so that when the pressure tank is "full" (at feed pressure) that valve closes off the feed and no more concentrate is produced.

 

[hio3791]

I'm in the market for an RO system so this is great info. Not trying to hijack the thread as the OP has specific questions. But I'm curious what systems would you guys recommend. As the OP mentioned, there are so many vendors, options, etc. Seems like more filters and higher flow rates is better.

 

[mongoose33]

To note a couple things in addition to AJ's fine answer:

If you look at the picture above in my post, you'll see three tubes: a blue one (source water from faucet), a white one (the RO output water I store in my Aquatainer), and a yellow one (this is the wastewater which I have going down the drain).

In an undersink system these are plumbed directly to source water, the tank storing the RO water, and the drain.

The question I'd have for you is whether any tank you use is large enough to store sufficient water for brewing. A typical brew for me uses 7 gallons of RO water plus 1 gallon of tap water. That's why the 7-gallon Aquatainer is a nice size for me.

 

[FatDragon]

@ajdelange - you're a legend. I will be referring back to that post through the process of buying this system. It's a lot of material to digest so it'll take a few readings but I think it should be all the information I need to make an informed purchase.

To note a couple things in addition to AJ's fine answer:

If you look at the picture above in my post, you'll see three tubes: a blue one (source water from faucet), a white one (the RO output water I store in my Aquatainer), and a yellow one (this is the wastewater which I have going down the drain).

In an undersink system these are plumbed directly to source water, the tank storing the RO water, and the drain.

The question I'd have for you is whether any tank you use is large enough to store sufficient water for brewing. A typical brew for me uses 7 gallons of RO water plus 1 gallon of tap water. That's why the 7-gallon Aquatainer is a nice size for me.

Discussion of water chemistry for brewing often comes down to "brew with RO water and mineral additions". I don't know of any source for bulk RO water here in Wuhan like the dispensers you can find in most supermarkets in the States, and "buy a cheap RO system" seems to be common advice around here, so I figured it must be an easy way to get RO water for brewing. It seems it's more complicated than all that, though. We'll be getting an RO system of some kind or other since my wife wants one, but now the question is whether or not I will use RO water for brewing. Right now I'm thinking I'll probably fill jugs or something like an aquatainer over the course of several days for brewing water, but I might just keep using tap water like the lazy dummy I am. Either way, it's helpful to understand RO systems so we can buy one for the house, whether or not it ends up producing brewing water.

 

[mongoose33]

Discussion of water chemistry for brewing often comes down to "brew with RO water and mineral additions". I don't know of any source for bulk RO water here in Wuhan like the dispensers you can find in most supermarkets in the States, and "buy a cheap RO system" seems to be common advice around here, so I figured it must be an easy way to get RO water for brewing. It seems it's more complicated than all that, though. We'll be getting an RO system of some kind or other since my wife wants one, but now the question is whether or not I will use RO water for brewing. Right now I'm thinking I'll probably fill jugs or something like an aquatainer over the course of several days for brewing water, but I might just keep using tap water like the lazy dummy I am. Either way, it's helpful to understand RO systems so we can buy one for the house, whether or not it ends up producing brewing water.

I suppose that you could get a couple containers and just fill them out of the tank over the course of a couple days.

Here's the other consideration: you'll have much more wastewater going down the drain than you will create RO water. If your local water is very expensive then it may or may not make sense to have an RO system.

Some of that can be mitigated by a sort of insert (can't recall the exact part) that replaces an existing insert, which reduces the amount of wastewater. But I think you can count on generating 3-5 times wastewater than what you get out as RO water.

If you haven't yet brewed with RO water, I think it's worth a shot getting some just to see if it makes a significant difference for you.

 

[ajdelange]

....you'll have much more wastewater going down the drain than you will create RO water. If your local water is very expensive then it may or may not make sense to have an RO system.

Some of that can be mitigated by a sort of insert (can't recall the exact part) that replaces an existing insert, which reduces the amount of wastewater. But I think you can count on generating 3-5 times wastewater than what you get out as RO water.

Items 5 and 7 in #5 above make it possible to recover half or a bit more of the feed as permeate without sacrifice of rejection. Item 8 makes it possible to recover 80% (1 gallon waste for every 4 gallons of RO water produced) with somewhat reduced rejection.

 

[Buckeye_Hydro]

There are practical uses for the concentrate (a.k.a reject water, or waste water). Many of our customers route it to their swimming pool, or into their home top loading washing machine.

Russ

 

[mabrungard]

There are practical uses for the concentrate (a.k.a reject water, or waste water). Many of our customers route it to their swimming pool, or into their home top loading washing machine.

I am rather leery of using RO wastewater for anything. Think of all the bad character of your tap water and multiply that by a factor of about 3 and you should see that the wastewater is going to be laden with a heavy load of ions. If you started with hard tap water, that wastewater is now super hard. I would never suggest washing clothing with it. If your RO feedwater is softened, the resulting wastewater is full of sodium or potassium. That might make it OK for washing, but it could kill plants in some cases.

Putting RO wastewater down the drain is not such a bad idea.

 

[Buckeye_Hydro]

Your point is a good one, but the quality of the brine is dependent upon the quality of the feedwater. Did laundry with mine for ~15 years.

 

[ajdelange]

As I recall in the BOQ's on Ascension Island the concentrate went to the toilets and showers and the permeate to the sinks, mess hall etc. To be honest about it I don't 100% remember that it was actually an RO system there but I do remember the facilities guy bellyaching about how much it cost him to produce a gallon of potable water.

 

[Buckeye_Hydro]

Was that a desalinization plant processing seawater?

 

[ajdelange]

Yes but as I say it was too long ago for me to remember how they did it. Thinking about it for a minute it wouldn't make much sense to send the concentrate to the toilets. It would make more sense to just use sea water.

 

[Buckeye_Hydro]

The concentrate at desalinzation plant is highly pressurized ~ 800 psi - maybe they wanted to capture that energy expenditure?

 

[ajdelange]

Possibly but they could do that by discharging back to the sea. All I really remember at this point was that we were told to be careful when driving as the feral donkeys on the island were crown property and we would be fined if we hit the queen's ass.