RO membrane and pre-filters - service life in 345mg/L very hard water

[LFNfan]

Hi All
I must be getting old as shifting 25L RO water jerry cans from A to B is not as trivial as it was even a year ago. So I am musing about splashing out on an RO system a la Osmotics, Vyair etc.

I did investigate this a while back and was thinking of RODI at that time. Having had the benefit of a year using RO from Spotless Water, I think RO meets my needs so I'm not planning on going the full DI route.

So, my question for ukaps members who use these sorts of RO systems in very hard water areas (eg 345 mg/L) is: do you see satisfactory results in terms of EC / TDS of the RO water produced by these systems with 'very hard' water as the input? And if so, does that depend on buying new RO membranes every few months (I am expecting to replace the pre-filters six-monthly)?

Many thanks in advance for any insights from experience!

 

[Bradders]

I am interested in this thread as well! Especially around the RO unit and how they cope with chlorine in the water which can destroy the membranes.

 

[LFNfan]

The chlorine will probably mostly be dealt with by the carbon pre-filter(s).

I think for me I'm more interested in hearing about experiences of how much of a beating the RO membrane takes from extracting the calcium and magnesium from my hard water, and how much this could shorten the membrane's service life. The trade-off for me will be between carting cheap RO water from Spotless Water vs making more expensive RO water at home! If I have to replace RO membranes every few months, that might be a point in favour of my current Spotless Water arrangements.

 

[dw1305]

Hi all,

So, my question for ukaps members who use these sorts of RO systems in very hard water areas (eg 345 mg/L) is: do you see satisfactory results in terms of EC / TDS of the RO water produced by these systems with 'very hard' water as the input?

There are quite a few variables, but as a general rule the harder the water is the more problems you have with membrane life and "scaling".

It is a bit of a silly question, but do you have an ion exchange (one that contains salt NaCl) water softener? If you do, you will get a lot longer life from the membrane.

The downside of this is that at least two out of every three litres of softened water will be lost during the RO process. We get through <"a lot of salt at home"> (without having an RO unit) and a lot of water (and consumables) at work via the <"DI filters">.

The trade-off for me will be between carting cheap RO water from Spotless Water vs making more expensive RO water at home!

There is a third option for those <"who can collect rainwater">, it is free and, pretty much, pure H2O at this time of the year.

cheers Darrel

 

[MichaelJ]

So, my question for ukaps members who use these sorts of RO systems in very hard water areas (eg 345 mg/L) is: do you see satisfactory results in terms of EC / TDS of the RO water produced by these systems with 'very hard' water as the input?

I produce about 250 liters of RODI water per month. My tap water varies between 250 and 350 ppm (mg/L). We do have a Potassium Chloride (KCL) based household softener in our house so most of the Ca and Mg is already removed but replaced by exorbitant amounts of K.... Our city water is about 17 dGH/dKH. Very hard water but varies over the year depending on the water source. Straight out the RO buddie 100 GPH I get about 4-5 ppm with the addition of a DI stage I get it down to 1 (the DI stage is largely unnecessary). Our water is not heavily chlorinated so the carbon filter will deal with it before it hits the membrane - high chlorine content (often mentioned) is not a real issue in terms of membrane longevity unless your tap water taste like swimming pool water - in which case an extra dechlorination pre-stage might be a good idea. I change all the cartridges (except for the more expensive membrane) when I see a significant spike on the outlet TDS which is usually every 9-12 months.

Cheers,
Michael

 

[MartyK]

I did investigate this a while back and was thinking of RODI at that time. Having had the benefit of a year using RO from Spotless Water, I think RO meets my needs so I'm not planning on going the full DI route.

So, my question for ukaps members who use these sorts of RO systems in very hard water areas (eg 345 mg/L) is: do you see satisfactory results in terms of EC / TDS of the RO water produced by these systems with 'very hard' water as the input? And if so, does that depend on buying new RO membranes every few months (I am expecting to replace the pre-filters six-monthly)?

Many thanks in advance for any insights from experience!

I have been using the same RODI system since 2007 and have never changed out the membrane; it has probably made tens of thousands of gallons of water in those 17 years. The source water has varied a lot as I moved but was generally above 200 ppm (ppm = mg/L) in all locations; at my current house, the well water is above 350 and sometimes 400+ depending on season. The source water has always been hard water that causes scaling on anything/everything it touches and has often been very iron rich as well leaving lovely brown stains too.

I have always had rejection ratios at or better than 98% prior to the DI stage which is exactly what the membrane is rated for. The only time the rejection rate dips is when the source TDS spikes high or when the prefilters are overdue for change. This is a bog standard RODI system with a Filmtec 75 gallons per day (GPD) membrane, 3 pre-filter stages, and 1 DI mixed-resin stage; the prefilters I run are usually 5 micron sediment, 1 micron sediment, and 5 micron carbon. Sometimes I have swapped out one of the sediment filters for another carbon filter due to chlorine or chloramine use in the source water but I don't have that problem with my current well water.

In terms of filter replacement, every six months is a good place to start but that may be too frequent depending on how much water you make. I usually change out the sediment filters twice as frequently as the carbon filters and they turn a nice orange/brown shade due to the iron. But, I also made some upgrades so I can monitor filter performance and that lets me go quite a bit longer than six months depending on my actual water usage.

Regarding the water softener question - I always hooked up the RODI system before the water softener in order to avoid wasting all that salt. Membrane life has never been a problem.

 

[MichaelJ]

I always hooked up the RODI system before the water softener in order to avoid wasting all that salt. Membrane life has never been a problem.

I actually wanted to do that originally as well, but only our outside taps bypasses the softener... never felt like spending the money on re-plumbing stuff down in our basement.

I have been using the same RODI system since 2007 and have never changed out the membrane; it has probably made tens of thousands of gallons of water in those 17 years.

Geez! Thats gotta be some sort of record!

Cheers,
Michael

 

[MartyK]

The manufacturers certainly want you to replace the membrane every 3 to 5 years but that usually assumes 365/24/7 use. I'd replace it if I started seeing worse rejection rates but it's still holding strong so I don't see any need. Sometimes I don't even need the DI stage. "If it ain't broke, don't fix it."

 

[bazz]

I think for me I'm more interested in hearing about experiences of how much of a beating the RO membrane takes from extracting the calcium and magnesium from my hard water, and how much this could shorten the membrane's service life.

Hi.
I live in Lincoln at the bottom of a jurassic limestone ridge where the tap water has a TDS of 340 and my Osmotics RO system (without a DI filter) reduces this to 10 TDS so I presume it has pretty much removed all of the calcium and magnesium. I change the prefilters approximately every 6 months but the actual membrane has now been running for almost 3 years and still produces the same TDS water as it did when I first used it. For reference I produce 155l a week.
Hope this helps,
Cheers!

 

[dino21]

I am interested in this thread as well! Especially around the RO unit and how they cope with chlorine in the water which can destroy the membranes.

As already mentioned a standard carbon block filter should remove the Chorine, but whats often not mentioned are the more problematic Chloramines, which takes a bit of investigation to find if your local water board is creating them , see -
*** | Anglian Water Services

So choosing the right Carbon Bock can avoid that problem, see these MatrixkX ones for example -
Search results for: 'mat'

 

[palcente]

My tap water is liquid rock. I use ion exchange softener on the mains and then feed that to RO. I use the system for my aquarium and for drinking water. After 12 months inline TDs meter indicates membrane is still good as new, but the taste of the water suggests otherwise. I tend to replace everything every 12 months based on that guess if you just use it for fish tank you can keep it going for years, nobody will ever complain.

 

[LFNfan]

Wow, thanks everyone. Extremely extremely helpful. Overall I think that puts me one step closer to going with an RO system.

do you have an ion exchange (one that contains salt NaCl) water softener?

No, no water softener.

third option for those <"who can collect rainwater">,

This is a tricky one. The best downpipe we have is at the back which would entail moving water from there to the tank which is at the front. I did have a look at one of these systems at the garden centre the other week - they look pretty good value for money. Not sure if they require other things to keep the water good - circulation pump, etc etc.

I change all the cartridges (except for the more expensive membrane) when I see a significant spike on the outlet TDS which is usually every 9-12 months.

Interesting. Good tip - thank you!

the prefilters I run are usually 5 micron sediment, 1 micron sediment, and 5 micron carbon.

Noted - thank you!

I always hooked up the RODI system before the water softener in order to avoid wasting all that salt. Membrane life has never been a problem.

That's good to know. I don't have a water softener so effectively I'd be in the same situation as you.

The manufacturers certainly want you to replace the membrane every 3 to 5 years but that usually assumes 365/24/7 use. I'd replace it if I started seeing worse rejection rates but it's still holding strong so I don't see any need.

I'd be producing about 30L a week, for just under a 50% WC. So pretty light usage compared to what most of you are doing.

the tap water has a TDS of 340 and my Osmotics RO system (without a DI filter) reduces this to 10 TDS so I presume it has pretty much removed all of the calcium and magnesium. I change the prefilters approximately every 6 months but the actual membrane has now been running for almost 3 years and still produces the same TDS water as it did when I first used it.

I would be happy with 10 TDS - that's about 20 μS or so I think. @bazz do you use two or three pre-filters in your Osmotics system?

For reference I produce 155l a week.

I'd be doing about 4 or 5 times less than that. Really good to know.

Chloramines

No chloramine as far as I can tell (Affinity water has seriously dumbed down the water report section of its website so I can't find the detailed report. But the 'simple version' refers to chlorine only.

guess if you just use it for fish tank you can keep it going for years, nobody will ever complain.

LOL.

 

[bazz]

I would be happy with 10 TDS - that's about 20 μS or so I think. @bazz do you use two or three pre-filters in your Osmotics system?

Three, 5 micron sediment, activated carbon and carbon block.

 

[dw1305]

Hi all,

Not sure if they require other things to keep the water good - circulation pump, etc etc.

Not really, I use the <"Daphnia bioassay">. Two water butts <"daisy chained together"> also helps.

These are the back garden butts. I've still got two of the three butts, but the "daisy chained" green-blue butt (far left) sprung a leak and I had to replace it. This image was pre-2011 (that was when we got solar panels on that roof), but the other two butts were already ~20 years old at that point and are still going strong. The single butt on the right was actually a repurpose chemical drum, so it has done really well.

cheers Darrel

 

[Calamardo Tentaculos]

@LFNfan you can always buy a generic RO filter from Finestfilters or any other online seller. As long as the measurements match, it is a much economical option.

Since I have the great fortune of having to rely on lovely London tapwater -with 330TDS, I decided to go with a 200 GPD five stage RO filter (3 pre-filters & 2 RO chambers) from Collins Water. The RO filters are in series so the waste from the first chamber goes into the second chamber, reducing waste and increasing my RO production (each filter is rated at 100GPD). I then add an Echen pump to increase pressure to about 80 PSI, reducing waste and increasing production further. If the water temps aren't too cold, I can have a RO to waste ratio of 1:1.5 which is much better than the 1:4 ratio that unpumped units produce.

Next, I will probably try to add a third RO stage in the future to see if it can be even more efficient.

Hope this helps.

 

[fredi]

@LFNfan you can always buy a generic RO filter from Finestfilters or any other online seller. As long as the measurements match, it is a much economical option.

Since I have the great fortune of having to rely on lovely London tapwater -with 330TDS, I decided to go with a 200 GPD five stage RO filter (3 pre-filters & 2 RO chambers) from Collins Water. The RO filters are in series so the waste from the first chamber goes into the second chamber, reducing waste and increasing my RO production (each filter is rated at 100GPD). I then add an Echen pump to increase pressure to about 80 PSI, reducing waste and increasing production further. If the water temps aren't too cold, I can have a RO to waste ratio of 1:1.5 which is much better than the 1:4 ratio that unpumped units produce.

Next, I will probably try to add a third RO stage in the future to see if it can be even more efficient.

Hope this helps.

I have a similar system from ro man, north kent tapwater, great for rift valley cichlids, but not much else

 

[Calamardo Tentaculos]

How hard is your water?

 

[dw1305]

Hi all,

north kent tapwater, great for rift valley cichlids, but not much else

<"https://www.stroodaquarist.co.uk/factsheets/">?

Personally if I used our tap water? I'd keep <"Lake Tanganyika cichlids">.

How hard is your water?

It is all about the same for people who get <"ground water from a limestone aquifer">, about 17 ~ 18 dGH and 17 ~ 18 dKH (so that is a lot of members in the SE. and E. of England).

It is just to do <"with Geology"> and the <"level of atmospheric CO2">. You can see the softer, less alkaline, water from the Weald in the two maps (one <"in the link">).

Here is the <"Water Hardness map"> for England and Wales.

cheers Darrel

 

[Calamardo Tentaculos]

Hi all,

View attachment 215719 <"https://www.stroodaquarist.co.uk/factsheets/">?

Personally if I used our tap water? I'd keep <"Lake Tanganyika cichlids">.

It is all about the same for people who get <"aquifer water from a limestone aquifer">, about 17 ~ 18 dGH and 17 ~ 18 dKH (so a lot of people in the S. and E. of England).

It is just to do <"with Geology"> and the <"level of atmospheric CO2">. You can see the softer, less alkaline, water from the Weald in the two maps (one <"in the link">).

Here is the <"Water Hardness map"> for England and Wales.

Thanks @dw1305! So going by the figures, is there an ideal water hardness that one should aim for when keeping planted tanks and most tropical fish? Should we be aiming to remineralise water to slightly hard or moderately soft?

 

[fredi]

Personally if I used our tap water? I'd keep <"Lake Tanganyika cichlids">.

Strange you should say that 😂😂😂