Why is RODI so much faster when it’s hot?

[BeanAnimal]

This is true, my main reason was to prevent the condensation on the unit in the summer which over time rusts the metal screws and bracket of the unit and drips on the floor.

Buy stainless screws... less expensive!

 

[Richsoar]

Every membrane I've used specifically says you'll ruin the membrane if you use "Hot" water.

 

[BeanAnimal]

Every membrane I've used specifically says you'll ruin the membrane if you use "Hot" water.

You don’t want to go over 100 degrees… 110 or a little warmer is considered hot by most standards.

 

[teleportinghere]

I thought I heard that hot water has higher TDS

Confirmed with a TDS pen just now. Just my personal results from the municipal water source in San Diego, CA, taken with a TDS pen.

Hot tap water: 735 TDS
Cold tap water: 445 TDS


This is heated from a water heater replaced in the last 2 years. I get my water to a safe 85*F as the cartridge manufacturer says anything over 90*F will cause rapid membrane failure. They also recommend replacing the carbon filter (rated for chloramine) every 6 months when processing chloramine treated water even under light use.

 

[Slocke]

Confirmed with a TDS pen just now. Just my personal results from the municipal water source in San Diego, CA, taken with a TDS pen.

Hot tap water: 735 TDS
Cold tap water: 445 TDS


This is heated from a water heater replaced in the last 2 years. I get my water to a safe 85*F as the cartridge manufacturer says anything over 90*F will cause rapid membrane failure. They also recommend replacing the carbon filter (rated for chloramine) every 6 months when processing chloramine treated water even under light use.

Funny how I also have a TDS pen and did not think to do this.

Thanks for sharing!

 

[Slocke]

Confirmed with a TDS pen just now. Just my personal results from the municipal water source in San Diego, CA, taken with a TDS pen.

Hot tap water: 735 TDS
Cold tap water: 445 TDS


This is heated from a water heater replaced in the last 2 years. I get my water to a safe 85*F as the cartridge manufacturer says anything over 90*F will cause rapid membrane failure. They also recommend replacing the carbon filter (rated for chloramine) every 6 months when processing chloramine treated water even under light use.

Also as someone who works for the EPA and knows the reputation of Californias environmental department and how heavy handed/funded it is. What on earth is wrong with San Diego water?!

 

[BeanAnimal]

Confirmed with a TDS pen just now. Just my personal results from the municipal water source in San Diego, CA, taken with a TDS pen.

Hot tap water: 735 TDS
Cold tap water: 445 TDS


This is heated from a water heater replaced in the last 2 years. I get my water to a safe 85*F as the cartridge manufacturer says anything over 90*F will cause rapid membrane failure. They also recommend replacing the carbon filter (rated for chloramine) every 6 months when processing chloramine treated water even under light use.

So you are cutting both your membrane life and DI resin life in half to increase production.

 

[Randy Holmes-Farley]

Confirmed with a TDS pen just now. Just my personal results from the municipal water source in San Diego, CA, taken with a TDS pen.

Hot tap water: 735 TDS
Cold tap water: 445 TDS


This is heated from a water heater replaced in the last 2 years. I get my water to a safe 85*F as the cartridge manufacturer says anything over 90*F will cause rapid membrane failure. They also recommend replacing the carbon filter (rated for chloramine) every 6 months when processing chloramine treated water even under light use.

I’m highly skeptical that the value is an actual tds rise as opposed to inaccurate (or no) temperature correction. It doesn’t make sense. Where would that 300 ppm tds be coming from?

Which pen? I’d check to see if it is correcting for expected temperature effects in measurement.

Take hot and cold tap water, let them both come to the same temp. Then compare them.

 

[Randy Holmes-Farley]

Funny how I also have a TDS pen and did not think to do this.

Thanks for sharing!

Do it properly by comparing them only once they reach the same temperature.

 

[Slocke]

I’m highly skeptical that the value is an actual tds rise as opposed to inaccurate (or no) temperature correction. It doesn’t make sense.

Which pen? I’d check to see if it is correcting for expected temperature effects in measurement.

Take hot and cold tap water, let them both come to the same temp. Then compare them.

I just repeated his experiment. I got 55 on cold water and initially 95 on hot but as the water is cooling the TDS is decreasing. It is now 75

 

[Randy Holmes-Farley]

I just repeated his experiment. I got 55 on cold water and initially 95 on hot but as the water is cooling the TDS is decreasing. It is now 75

Which device are you using? Many tds devices, such as the inline devices, aren’t temp corrected at all (and so will read off for temps other than 25 deg C).

 

[Slocke]

Which device are you using? Many tds devices, such as the inline devices, aren’t temp corrected at all (and so will read off for temps other than 25 deg C).

CIZTADA it does also measure temperature but I don’t know if it corrects for it

Still waiting for hot water to cool and the TDS is still decreasing if more slowly.

 

[Randy Holmes-Farley]

what sorts of temp difference? Is the cold one warming?

 

[BeanAnimal]

I’m highly skeptical that the value is an actual tds rise as opposed to inaccurate (or no) temperature correction. It doesn’t make sense. Where would that 300 ppm tds be coming from?

Calcification and scale in the hot water tank. The inlet tube is at the bottom and the discharge at the top. Both the convective currents and the inlet water keep the solids stirred up, to which I assume some redisolve. There is also often some corrosion and always a sacrificial anode to help prevent the corrosoin.

So I would assume some people will def have higher TDS from water that went through the heater. I guess it would depend on the age and state of the tank.

 

[Slocke]

what sorts of temp difference? Is the cold one warming?

This is taking a while as it takes 5+ minutes for the temperature to adjust on the meter
Cold 74.4F - 60 TDS
Hot 87.8F - 67 TDS

 

[Randy Holmes-Farley]

Calcification and scale in the hot water tank. The inlet tube is at the bottom and the discharge at the top. Both the convective currents and the inlet water keep the solids stirred up, to which I assume some redisolve. There is also often some corrosion and always a sacrificial anode to help prevent the corrosoin.

Corrosion will add a little tds but the dissolution of precipitated solids is not a generally tds raising process since it has to drop to form those solids in the first place.

 

[Randy Holmes-Farley]

This is taking a while as it takes 5+ minutes for the temperature to adjust on the meter
Cold 74.4F - 60 TDS
Hot 87.8F - 67 TDS

Thanks. Looks to be coming close together. The cold is very near the normally accepted temp for conductivity, 25 C.

 

[BeanAnimal]

Corrosion will add a little tds but the dissolution of precipitated solids is not a generally tds raising process since it has to drop to form those solids in the first place.

I would think that over time, accumulation could get worse? I have seen tanks with 6-10 inches of sediment. Also water quality here does go up and down depending on season, etc, They also change is from chlorine to chloramine every so often I think. No clue what that means for dissolution. Anyway, just thoughts. Looks like temp has a lot to do with the meter accuracy?

 

[Randy Holmes-Farley]

I would think that over time, accumulation could get worse? I have seen tanks with 6-10 inches of sediment. Also water quality here does go up and down depending on season, etc, They also change is from chlorine to chloramine every so often I think. No clue what that means for dissolution. Anyway, just thoughts. Looks like temp has a lot to do with the meter accuracy?

I suppose there may be times when hot water tds is lower than cold (due to net formation of deposits) and times when it is higher (due to net dissolution of solids). But the solids can’t be viewed as always adding tds.

 

[teleportinghere]

I’m highly skeptical that the value is an actual tds rise as opposed to inaccurate (or no) temperature correction. It doesn’t make sense. Where would that 300 ppm tds be coming from?

Take hot and cold tap water, let them both come to the same temp. Then compare them.

Ah, the temperature! Now at similar temperature hours later, they are at:

Hot tap water (now @74*F): 445 TDS
Cold tap water(now @72*F): 420 TDS

Fascinating, thanks Randy.

So you are cutting both your membrane life and DI resin life in half to increase production.

A little less since its mixing temperatures (100% output of cold + ~30% output of Hot). But yeah, the amount of reject water was much greater on cold only. I personally justify slightly less life out the membrane to not put all that water down the drain.