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'by The Numbers..' Help With Ro System Please?

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Hey folks.


I have a little 50gpd RO system i've set up in my house, just for filling barrels and etc. I've been doing some number crunching with it, and I think something may be wrong!


I timed how long it took to produce a litre of pure water. Pretty much 20 minutes, on the nose.


So, that means it's producting 5 litres per hour of pure water. So 5 hours for a 25 L drum..


I also measured the waste water. It was about 6 litres, rounding down a little bit. So that's producing 30L of waste water per hour, meaning about 150L of waste water for 25L of pure water. Working out percentages, I come up with 16% (ish) pure water, 84% (ish) waste water.

Do these numbers sound right? Seems like a very slow, and wasteful way to get pure water.. 5 hours for a 25 litre drum? if I wanted to go out with say 250L of water, then - I'd need to fill for 50 hours? And I'd waste 1,500 Litres of water??!!



What the....???!!!!!

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As Tuffers has suggested, your pure figures are incorrect. I would also guess that the waste figure is also suspect.


I don't know what system you have, but the usual way of 'throttling' the waste is with a 3 to 1 inline restrictor which is what we had. You need to restrict the waste so that you get a 3 litre waste output to 1 litre of pure. Remember your 50GPD r/o is optimum (water temperature and water pressure) over a 24 hour period. They are also American gallons which aren't the same as imperial gallons (smaller).


Once you get the waste to pure ratio right, you will produce more pure provided you have a decent water pressure.


IMHO a 50GPD r/o is a complete waste of time for window cleaning. In the winter it will produce 1/2 of what it is now with the colder tap water temperatures.


Daqua are advertising a 300GPD unit at a very good price - the 450GPD is only £20.00 more which I would recommend. Process into an IBC tank and use a submersible to fill your containers/tank. You would just need to connect a water timer to the supply tap for it to switch off in X number of hours.

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Yeah, it's only 40PSI, I have been looking into a booster pump but we have a 'proper' system on the van, I was just setting this one up half out of boredom and half so we have a backup and can do work with backpacks if anything ever happens to the van etc as a short term fix.


Ok so, as someone pointed out, my figures are ****, way out. I will redo them but not now as I'm tired and i'm having a beer as I have tomorrow off!


Has anyone seen those 'low pressure' RO filters, are they any good? If I spend 30 quid on a 150gpd one, will that make the difference? since it is designed to work at my houses PSI?



Basically can someone wise tell me how to fix it, I am not skilled when it comes to these matters... lol


Buying a new RO system would of course fix it, but I want to spend the least amount possible, remember this is only for backup, for filling a few barrels if the need arises etc. If I could filter about 250L a day without using up half an ocean i'd be happy.

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That 150 GPD membrane will go into your housing. Get an inline resistor and you will be up and away. We used a 450GPD r/o on 40/50 psi for years without a booster pump. Yes, water production wasn't as fast, but as a backup spending money on booster pumps is probably going too far. Our water TDS was 255 and pure was 4/5 ppm. After all mains were relined, our tap tds dropped to 115 and our r/o was producing pure at 2ppm.

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Kips I was in a similar situation as you however my original system was a 100gpd.


I've just found these photos that i took whilst upgrading my system last summer. It kinda gives you an idea of the difference between systems and using a booster pump.



Original 100gpd system




Original 100gpd with booster




Upgraded to 200gpd




200gpd with booster




Each photo was taken over 20mins. Waste is on the left and pure is on the right.


Hope it uploads ok using my iphone!





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