DI Vs RO

jgrayson11 · Jun 4, 2018

Hi all,

Recently moved house after getting a steady 50-60ppm to a now steady 150-160ppm out the tap.

Obviously resin costs have gone up, but wanted to know your thoughts on staying with DI or switching to RO?

Never used RO before and am not truly sure of the efficiency or cost, but has anyone made this transition before (where tap water ppm has shot up singificantly and you opted to change)?

Just after some advise to figure out what the most cost effective way of purifying my new tap water will be, as would rather switch, if need be, sooner rather than later to become more efficient.

I understand RO takes much longer to work, but that's fine. Have gotten used to the glorious nature of DI over the years and never needed to consider the cost as resin would last a while.

All replies very welcome!

Cheers

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spruce · Jun 4, 2018

Only you can make the decision. It doesn't help that you have given us little information in your post such as how much water you use a week/month or if you are on a water meter etc. What is your tap water pressure?

Personally, I think you need to go r/o but depending on water usage, water cost and your competence, it may be better to stay with di.

From a good quality r/o you should expect the r/o membranes to remove between 97 - 98% of the dissolved solids in the water. But an r/o needs to flush away impurities its removing with waste water to the drain whilst its purifying pure. So you need to expect to send 1 liter of water to the drain whilst producing 1 liter of pure = 2 liters of water.

So your costs have to include the total amount of water you need to buy if you are on a meter for comparison purposes.

Personally, I believe the smallest r/o you should consider is a 450gpd which will also give you a little room production wise for expansion.

Included in your costing would be the cost of the r/o, an IBC tank to process water into and a submersible transfer pump to pump water into the van. You also need a place to store the equipment as well as giving frost protection in the winter months. I also think you need to consider an auto cut off system so the r/o stops working when your storage tank is full.

You know how much resin is costing you now. Polishing the remaining 2 - 3% of tds will reduce resin costs considerably. You can use a resin calculator to calculate expected future resin costs if you use an r/o. Google "resin calculator".

jgrayson11 · Jun 4, 2018

Thanks for your quick reply@spruce.

I am not on a water meter. I use about 600L per day. Not sure of tap pressure but it is exceptionally good!

Happy to store an IBC tank. I also have room to keep a new system indoors (well insulated outbuilding that has mains power but no heating).

Are they any r/o systems you could recommend to me?
Alternatively, I read recently about softening the water before running through DI - do you or anyone else have experience with this as I'd be interested to find out more?

Cheers

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spruce · Jun 4, 2018

jgrayson11 said:
Thanks for your quick reply@spruce.

I am not on a water meter. I use about 600L per day. Not sure of tap pressure but it is exceptionally good!

Happy to store an IBC tank. I also have room to keep a new system indoors (well insulated outbuilding that has mains power but no heating).

Are they any r/o systems you could recommend to me?
Alternatively, I read recently about softening the water before running through DI - do you or anyone else have experience with this as I'd be interested to find out more?

Cheers

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Using 600 liters per day means you are going to have to go for an r/o that's bigger than a 450gpd imho. I think you need to be looking at either a 4021 or a 4040. However, if you went for a smaller r/o there could be times when you would have to top the system up with di only.

Water softeners don't reduce tap water tds. They remove calcium and magnesium ions from the water and replace them with sodium ions. So the water coming out of the softener will have exactly the same tds as the water going in. A water softener will make no difference to you if you continue using a di vessel.

If you lived in a hard water area, then a water softener would help extend the life of your r/o membrane. But its all about balancing costs and effort. If it was going to cost you £200 a year to maintain a softener, then it could well be less hassle and more cost effective to buy a replacement membrane a little more often.

jgrayson11 · Jul 1, 2018

spruce said:
Using 600 liters per day means you are going to have to go for an r/o that's bigger than a 450gpd imho. I think you need to be looking at either a 4021 or a 4040. However, if you went for a smaller r/o there could be times when you would have to top the system up with di only.

Water softeners don't reduce tap water tds. They remove calcium and magnesium ions from the water and replace them with sodium ions. So the water coming out of the softener will have exactly the same tds as the water going in. A water softener will make no difference to you if you continue using a di vessel.

If you lived in a hard water area, then a water softener would help extend the life of your r/o membrane. But its all about balancing costs and effort. If it was going to cost you £200 a year to maintain a softener, then it could well be less hassle and more cost effective to buy a replacement membrane a little more often.

After much debate and research, I finally decided upon Daqua's 4021 RO system. So far so good - water quality is great, very happy with the quality of the whole set up. I've read many articles about changing the sediment and carbon filters, along with the RO membrane, and can't seem to find a solid (or even general) answer. Can anyone give an idea as to how I will be able to identify when the sediment and carbon filters will need changing? I'd imagine it becomes quite apparent with water quality degredation over time, but since everything is ultimately being finished with DI at the end of the filtering process, I'm not sure what to look out for?

Any answers very much appreciated.

Thanks in advance.

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Part Timer · Jul 1, 2018

Your pre filters need to be changed regularly, depending on how much water you use. The membrane needs to be flushed and it will tell you, when the TDS goes up, that it needs changing.

spruce · Jul 1, 2018

I have a similar flow counter to this @jgrayson11

http://gardinerpolesystems.co.uk/all-products/pure-water-systems/water-treatment/tds-meters/digiflow-flow-meter-and-filter-life-monitor-with-1-2-ports.html

The one I have counts backwards to zero. I have 20" prefilters and use Fiberdyne carbon block filters which have a service life of 75700 liters which is the total of waste plus pure. So I set the count down counter to 76000 liters and change the prefilters when the alarm goes off when the counter reaches zero. The alarm is an audible bleep. I change those filters every 3 to 4 months based on our water usage.

If you have 10" Fiberdyne filters then their service life is about 38000 liters. Some cheaper carbon block filters only have a service life of 10,000 liters, so they must be changed more regularly. In our case it would be every 12 to 16 days if we follow the manufacturer's instructions.

Sometimes our tap water is laden with silt and the sediment filter blocks up very quickly. I have a visual as I ordered clear filter bowls so can see the sediment discolourisation of the sediment filter. I also have a pressure gauge mounted each side of the prefilters. ATM our water pressure is 50psi and when the prefilters are new the pressure gauge after the carbon block will read 50psi as well. When the sediment filter starts to restrict the flow of water through the prefilters is when I change the sediment filter. My change point is at 40psi - so I'm loosing 10 psi. Anything below that affects my pure water quality.

In most instances we change both the sediment and prefilters at 75700 liters. But on occasion I've had to replace the sediment filter once a month. In fact I got caught once and had to replace the sediment filter after 3 days.

As per @Part Timer with regard to changing the membrane. I have an inline tds meter that has 2 sensors. The first is on the pure line leaving to r/o and the second is after the di vessel.

With our water tds at 123ppm atm the tds of the pure after r/o fluctuates between 2 and 3. That equates to a membrane efficiency of 98%. Its been like that since new and in 2 months the membrane will be 6 years old. When the efficiency of the membrane drops to about 94% is when I would consider to replace the membrane, but its all about economies of scale. Currently 6 liters of resin in my di vessel lasts me a year. If the resin lasted me 10 months at 94% membrane efficiency, it would probably still be worth spending a little extra on resin than forking out a lot more for a replacement membrane. So its hardly worth spending £320 on a new 4040 membrane when the resin is costing an extra £15 a year. In the old days a brand new Merlin r/o ran at an efficiency of 90%.

But the picture would be different if my water tds was 550ppm as it is in Hartlepool. The difference between 98% efficiency ( 11ppm), 94% efficiency (33ppm) and 90% (55ppm) would add a lot more to the cost of polishing those extra 44ppm off. I would probably replace the membrane sooner rather than later.

.

Jordiebarrett · Jul 1, 2018

spruce said:
I have a similar flow counter to this [mention=5144]jgrayson11[/mention]

http://gardinerpolesystems.co.uk/all-products/pure-water-systems/water-treatment/tds-meters/digiflow-flow-meter-and-filter-life-monitor-with-1-2-ports.html

The one I have counts backwards to zero. I have 20" prefilters and use Fiberdyne carbon block filters which have a service life of 75700 liters which is the total of waste plus pure. So I set the count down counter to 76000 liters and change the prefilters when the alarm goes off when the counter reaches zero. The alarm is an audible bleep. I change those filters every 3 to 4 months based on our water usage.

If you have 10" Fiberdyne filters then their service life is about 38000 liters. Some cheaper carbon block filters only have a service life of 10,000 liters, so they must be changed more regularly. In our case it would be every 12 to 16 days if we follow the manufacturer's instructions.

Sometimes our tap water is laden with silt and the sediment filter blocks up very quickly. I have a visual as I ordered clear filter bowls so can see the sediment discolourisation of the sediment filter. I also have a pressure gauge mounted each side of the prefilters. ATM our water pressure is 50psi and when the prefilters are new the pressure gauge after the carbon block will read 50psi as well. When the sediment filter starts to restrict the flow of water through the prefilters is when I change the sediment filter. My change point is at 40psi - so I'm loosing 10 psi. Anything below that affects my pure water quality.

In most instances we change both the sediment and prefilters at 75700 liters. But on occasion I've had to replace the sediment filter once a month. In fact I got caught once and had to replace the sediment filter after 3 days.

As per [mention=2712]Part Timer[/mention] with regard to changing the membrane. I have an inline tds meter that has 2 sensors. The first is on the pure line leaving to r/o and the second is after the di vessel.
With our water tds at 123ppm atm the tds of the pure after r/o fluctuates between 2 and 3. That equates to a membrane efficiency of 98%. Its been like that since new and in 2 months the membrane will be 6 years old. When the efficiency of the membrane drops to about 94% is when I would consider to replace the membrane, but its all about economies of scale. Currently 6 liters of resin in my di vessel lasts me a year. If the resin lasted me 10 months at 94% membrane efficiency, it would probably still be worth spending a little extra on resin than forking out a lot more for a replacement membrane. So its hardly worth spending £320 on a new 4040 membrane when the resin is costing an extra £15 a year. In the old days a brand new Merlin r/o ran at an efficiency of 90%.

But the picture would be different if my water tds was 550ppm as it is in Hartlepool. The difference between 98% efficiency ( 11ppm), 94% efficiency (33ppm) and 90% (55ppm) would add a lot more to the cost of polishing those extra 44ppm off. I would probably replace the membrane sooner rather than later.

.

I'm ashamed Spruce... You're going 300L over the recommended figure :O

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