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Old 21-05-2018, 12:52 PM   #1
Georgy
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Reverse Osmosis Water

Does anyone use RO water for rinsing? I notice most seem to be using DI units but I don't think these remove the limescale
After rinsing the car I used to use a watering can to pour RO water over the car, as its totally pure water there are no water spots.
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Old 21-05-2018, 12:59 PM   #2
puntohgt77
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I've used a D.I resin vessel for the past 2 years to do a final rinse on my car without the need for drying and just leave it to dry naturally.

It leaves it completely mark/spot free. I just use a hozelock sprayer on the end of another hose pipe on mine.

I've just had a buy another bag of resin (tulsion mb115) which was £80 for 25kg but has lasted me nearly 2 years with 2 cars being washed weekly.
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Old 21-05-2018, 05:53 PM   #3
westerman
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RO water is great and it's pure. I used to use RO water in my aquatics business and also sold gallons of the stuff. Problem with installing your own system is that only a small amount of the water that enters it is purified (around 10%) the rest goes down the drain, so if you're on a water meter or are Eco friendly, it's not the best.

Harry
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Old 21-05-2018, 06:55 PM   #4
fatdazza
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RO water is fine, but as earlier op says the trouble is the recovery rates are low (and often lower than membrane manufacturers quote.

Di vesels are perfect for final rinse. The limescale is disolved ions of calcium carbonate. A mixed bed DI vessel removes anions and cations and hence the water will have no disolved solids and therefore there will be no water spots.
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Old 24-05-2018, 11:23 AM   #5
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For car cleaning i wouldnt bother with an RO unit. If you want to use RO find a local aquatics shop that specializes in marine (saltwater) fish and ask them how pure it is.

I have my own aquatics shop and we make 0tds water and i have used it in the past to rinse car and i always use it in screen wash and coolant.

FYI we sell it @ £3.50 for 25L so its not expensive.

If you are using more than about £100 per week then your own unit will be more cost efficient but anything less and its not. They still use DI Resin but as its after the membrane it last significantly longer
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Old 25-05-2018, 09:02 PM   #6
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I’ve seen RO units with DI as the final stage for under £200 - would that not be more cost effective? Or maybe these sub £200 setups would not be adequate?

Thanks.
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Old 25-05-2018, 09:09 PM   #7
fatdazza
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Quote:
Originally Posted by keithjmason View Post
I’ve seen RO units with DI as the final stage for under £200 - would that not be more cost effective? Or maybe these sub £200 setups would not be adequate?

Thanks.
1. RO units waste a lot of water (can be as high as 90% loss)

2. Flow rates from small RO units will be low (too low for final rinse) so you will have to store the RO water in a tank and then rinse from the tank.
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Old 25-05-2018, 09:16 PM   #8
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Yeah, I have 2 water butts. I was thinking to have the RO water go to one for final rinse and the ‘waste water’ going to the other for eco-ness and water the garden. Plus not on a water meter.
By 90% loss I assume that for example, every litre of tap water that goes in, 100ml comes out as pure, and 900ml is waste ?

Thanks.
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Old 25-05-2018, 09:34 PM   #9
fatdazza
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Quote:
Originally Posted by keithjmason View Post
Yeah, I have 2 water butts. I was thinking to have the RO water go to one for final rinse and the ‘waste water’ going to the other for eco-ness and water the garden. Plus not on a water meter.
By 90% loss I assume that for example, every litre of tap water that goes in, 100ml comes out as pure, and 900ml is waste ?

Thanks.
Yes you are correct about recovery rates. They do vary and depend on the units and the water pressure. RO membranes work best under higher pressure.
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Old 12-07-2018, 10:50 AM   #10
keithjmason
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Have started to play around with RO
Just a quick question. Does the incoming water pressure impact the TDS of the water that comes out the membrane ?
From my understanding, the water pressure would affect flow rate and % of water ‘wasted’ only.
My water pressure is not that high, but within the spec of what the membrane needs. I’ve run it at a few different pressures (night seems to have higher pressure than daytime) and the TDS out the membrane remains pretty constant.

The reason I ask is that TDS out the membrane is 22 (input water is 342) and I was expecting it to be lower - possibly as issue somewhere, or is this actually expected ?
At this TDS, I would be replacing the resin in the little final stage filter very very often.

Any advice I would be very grateful.

Also I went for the 75 GPD membrane. Water pressure has been between 3 and 4 bar during testing. And always water out the membrane is 22 TDS

Membrane quotes 97.5% - and so I would think the water out should be closer to 9 TDS
Maybe I’ve got something wrong in my understanding though.

Thanks
Keith

Last edited by keithjmason; 12-07-2018 at 10:53 AM.
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