RO/DI with water softener questions?

[berry79]

Searched but, couldn’t find much info. I live in south Florida with some pretty hard water. I have a kinetico water softener system installed for my house water but, also have one spigot out side that bypasses the water softener for washing the vehicles. I use a DI unit for washing the cars and the DI media seems to last longer when bypassing the softener, hence the one spigot outside. I have the RO buddy on order and I’m wondering what would be better for the tank and filter. Should I connect to the softened water or would it be best connected to the bypassing spigot. Only issues with the spigot is that it’s outdoors and would have to leave the ro buddy exposed to the outdoor elements while I’m filtering the water. I would then store it inside. Thanks for any help

 

[KStatefan]

Soft water is better for the RO membrane

 

[Midrats]

Spectrapure advised me in the Nineties to use softened water.

 

[regionreef219]

I have a similar set up. Really hard water from the city. If I used the tap water straight it would wear out membrane much quicker since it would have a lot of ppm to reduce. Although the water softener adds a touch of salt to the water, it drops the ppm count drastically and then the membrane in the RODI unit has a much easier time and lasts longer.

I would connect your RODI unit after the water softener and not think twice.

 

[berry79]

Perfect. Thanks for the help. It would definitely be easier to connect after the softener. That’s what I was hoping to hear.

 

[anthonygf]

Is this the type of system you need to use salt? What is your TDS before and after the softener? I get better results from my RO/DI system since I switched to potassium chloride from the sodium chloride. Potassium is more expensive but is better for the RO membrane.

 

[berry79]

Is this the type of system you need to use salt? What is your TDS before and after the softener? I get better results from my RO/DI system since I switched to potassium chloride from the sodium chloride. Potassium is more expensive but is better for the RO membrane.

Yes it uses salt and also has carbon canister as well. Not sure what the TDS is at the moment. Waiting for a tester. I have one on my car wash DI unit but it’s in-line and only reads TDS after the filtration which is 0.

 

[anthonygf]

Yes it uses salt and also has carbon canister as well. Not sure what the TDS is at the moment. Waiting for a tester. I have one on my car wash DI unit but it’s in-line and only reads TDS after the filtration which is 0.

I hear it is best to have the carbon before the softener, the chlorine breaks down the softener resin. I had a softener years ago and the resin/beads disintegrated and fouled up my post sediment filter because I had the carbon after the softener.

 

[berry79]

I believe my carbon is before the softener side. We had kinetico come in and install the unit after the house was built and before we moved. They have a pretty good reputation down here and the unit has been great at reducing hard water.

 

[Randy Holmes-Farley Verified Community Expert]

I have a similar set up. Really hard water from the city. If I used the tap water straight it would wear out membrane much quicker since it would have a lot of ppm to reduce. Although the water softener adds a touch of salt to the water, it drops the ppm count drastically and then the membrane in the RODI unit has a much easier time and lasts longer.

That's not the reason.

A water softener does NOT decrease the ppm TDS of the water. It actually increases it a little bit as it swaps in two sodium ions for one calcium or one magnesium.

What it does do is greatly decrease the tendency for calcium and magnesium carbonate to precipitate onto or into the RO membrane, clogging it. Thus, the softener prolongs the membrane lifetime.

The trade off is it may deplete the DI a little faster since sodium gets through a RO membrane a little more readily than does calcium or magnesium.

 

[Euphylliafreak]

I live in the middle of nowhere and have well water. It goes threw a water softener. And then threw my 6 stage rodi filter and at the end I have a silicate remover bc I found out that my water was full of it and was causing me issues in my water. I called bulk reef supply and they helped me greatly and advised me that if you running a softener you should run the silicate remover as well. And plus it’s extra filtration to ensure your water is AWESOME

 

[Nexus_]

That's not the reason.

A water softener does NOT decrease the ppm TDS of the water. It actually increases it a little bit as it swaps in two sodium ions for one calcium or one magnesium.

What it does do is greatly decrease the tendency for calcium and magnesium carbonate to precipitate onto or into the RO membrane, clogging it. Thus, the softener prolongs the membrane lifetime.

The trade off is it may deplete the DI a little faster since sodium gets through a RO membrane a little more readily than does calcium or magnesium.

What do you know about potassium vs sodium for the R.O. membrane?

 

[Nexus_]

What do you know about potassium chloride vs sodium chloride for the R.O. membrane?

 

[Nexus_]

Is this the type of system you need to use salt? What is your TDS before and after the softener? I get better results from my RO/DI system since I switched to potassium chloride from the sodium chloride. Potassium is more expensive but is better for the RO membrane.

I've been wondering about this. Do you know why it's better?

 

[Randy Holmes-Farley Verified Community Expert]

What do you know about potassium vs sodium for the R.O. membrane?

Not sure what question you are exactly asking, but both sodium and potassium are well rejected by an RO membrane.

The reason to have a water softener in front of the RO membrane when one has hard water is to prevent calcium carbonate formation on the membrane, fouling it. That softener use may come at a very slight cost in raising the number of ions that the DI needs to remove.

 

[Randy Holmes-Farley Verified Community Expert]

I've been wondering about this. Do you know why it's better?

I do not think that is a generally true result.

 

[PapaFishRocks]

Straight up, I have learned more from Randy’s posts, than I could ever imagined.

I’m an engineer and love to know the “why” behind things.

Thank you so much for being here to explain. It is truly appreciated.

 

[Buckeye Hydro Verified Sponsor]

When we spec/sell/install large commercial RO systems, in nearly all cases we also spec/sell/install a water softener (as well as a backwashing carbon tank) ahead of the RO. Why?

As mentioned above, hardness in the water will "scale" a membrane ("fouling" a membrane is a term generally used to describe the clogging of a membrane due to bacteria). Just like the scale that may form around your kitchen faucet, the RO element will fill with this same scale and the system user will see decreased permeate production. Typically, the scale will also abrade/physically damage the membrane and higher TDS permeate will result.

Most higher capacity RO systems are configured to operate at about a 50% recovery - meaning about a 1:1 ratio of concentrate to permeate. We're able to operate these systems like this because all the scale forming minerals are removed by the softening pretreatment. If you read the fine print in the manual of a commercial RO system, you'll likely see that the required feedwater parameters include "Total Hardness at less than 1 grain per gallon" (~17 ppm).

If you have hard water and try to operate a residential RO system with something like a 1:1 ratio you will no doubt shorten the usable lifespan of the membrane. Because residential-scale RO systems are typically installed with very limited knowledge re the quality of the feedwater, these RO systems are typically configured at a 3:1 to 5:1 concentrate to permeate ratio. This is done to help avoid the deposition of scale within the membrane element.

Russ

 

[Reefer1978]

Not a scientific response but just real world experience. I have very hard water, 500-600 TDS, and prior to installing the water softener RO output was between 50-60 TDS and of course I was burning through DI resin, 1 cartridge per 50 gallons.

After installing the water softener with a carbon bed, RO output is 7-10, DI lasts for 200-300 gallons.

 

[Randy Holmes-Farley Verified Community Expert]

Not a scientific response but just real world experience. I have very hard water, 500-600 TDS, and prior to installing the water softener RO output was between 50-60 TDS and of course I was burning through DI resin, 1 cartridge per 50 gallons.

After installing the water softener with a carbon bed, RO output is 7-10, DI lasts for 200-300 gallons.

Was this well water? Unless the softener removed CO2 in some way that was significant, I think the result may not be generally applicable since I do not believe there's a mechanism for a softener to increase the RO membrane efficiency.