Hot or cold water for rodi

[Jvesche20]

I just got a new place and I’m trying to hook up everything. The only place I can hook up my rodi unit is from the washing machine. So with that being said it’s either hot or cold water. I tried the hot water but it seems to get very hot so I don’t know if that’s fine or should I just stick with the cold water side.

 

[GabeM]

Cold...

 

[The Aquatic Arsenal]

Cold

 

[Peace River]

Cold

+1

You run the risk of damaging the RO membrane if you use hot water, but that will at least partially depend on how hot the hot water is. Additionally, hot water often has more impurities that your system will need to filter out.

 

[Jvesche20]

+1

You run the risk of damaging the RO membrane if you use hot water, but that will at least partially depend on how hot the hot water is. Additionally, hot water often has more impurities that your system will need to filter out.

Awesome its pretty hot so i just changed it to cold water

 

[mfinn]

Awesome its pretty hot so i just changed it to cold water

How much hot water did you run through the unit before changing it to the cold side?

 

[Jvesche20]

How much hot water did you run through the unit before changing it to the cold side?

i ran it for 1-2 minutes at most and realized I had used the hotwater not cold then turned it off so not much water.

 

[jeffchapok]

I agree on cold. If you've ever drained a hot water heater, you know all the minerals that build up in the bottom of one of them. No sense in making your RODI work that much harder to get it all out.

 

[mfinn]

i ran it for 1-2 minutes at most and realized I had used the hotwater not cold then turned it off so not much water.

Hot water can damage the membrane. I have no idea how long of exposure does damage, but hopefully only a minute or so doesn't hurt.
If you have high TDS readings after the membrane, more investigation might be required.

 

[Colt13]

Pretty sure if it’s 113 degrees for even a few seconds the membrane will be trashed

 

[MabuyaQ]

I agree on cold. If you've ever drained a hot water heater, you know all the minerals that build up in the bottom of one of them. No sense in making your RODI work that much harder to get it all out.

You do realize that all came in with cold water feeding you heater. It is the stuff (and more) a RODI unit is going to remove from that same cold feedwater.

Flux/flow values given by manufacturers are measured at 25C. And for every 1C lower you lose around 3% of flux/flow. Depending on membrane material they can be operated at temperatures up to 30C-35C, but any higher even for a brief moment will permanently impact performance and can render them useless. So depending on how hot hot was in this case you may be save or TDS will go up and you need to replace the membrane.

 

[jeffchapok]

You do realize that all came in with cold water feeding you heater. It is the stuff (and more) a RODI unit is going to remove from that same cold feedwater.

Good point. But intuitively I've got to think that 40 gallons of 110 deg plus water sitting in there with all those minerals is still going to have a higher TDS than the water supply feeding into it.

 

[Jvesche20]

Hot water can damage the membrane. I have no idea how long of exposure does damage, but hopefully only a minute or so doesn't hurt.
If you have high TDS readings after the membrane, more investigation might be required.

checked the water and its reading 0 tds

 

[Opus]

checked the water and its reading 0 tds

Not a good indicator if that is after the di. You need to measure your tap tds and tds after the membrane to determine if your membrane is working properly.

 

[MabuyaQ]

Good point. But intuitively I've got to think that 40 gallons of 110 deg plus water sitting in there with all those minerals is still going to have a higher TDS than the water supply feeding into it.

Nope it is actually lower. With the raising temperature HCO3 will start reacting with itself resulting in CO3 and less CO2.This will induce precipitation of Ca and Mg as CaCO3 and MgCO3 which wouldn't have to be removed by the RODI membrane/prefilters. The resulting calciumcarbonate and magnesiumcarbonate (and anything trapped in this precipitate) won't dissolve under normal circumstances. Hence the buildup in heaters, boilers and your waterkettle in the kitchen.