[easy clean]

whilst working today one of my many ideas was, would it work to put water that comes out the ro at 10, put it back into a 2nd ro at 10 and then purify it a further 95-98%

any thoughts welcome

would deff save a few quid on resin

[RPCCS]

if its coming out @ 10 do you really need to bother re filtering it , everyone says tds of 10 is still workable

[clean]

I don`t think there would be enough pressure coming out of the RO to go into another RO   

[Peter Fogwill]

You wold have to pump it through for a start, and you would only have around 1L for 10L of tap water.  Stick with the way it is already.

Peter

[RPCCS]

you'd probably end up changing your filters more often than you would with just 1 ro

[michael papworth]

There is a law called the law of diminishing returns. It would apply here, I think.

The cost of purifying water with an RO unit is about 60% product and 40% waste. Presumably the second RO would give similar results which would give a total of 36% product and 64% waste - and the tds of the waste from the second unit would only be about 20 ppm so you're throwing away very pure water.

Stick to DI, it's easier and probably cheaper in the end.

[Peter Fogwill]

i understand what your saying peter but would it purify it more and more each time thus eliminating the use of resin

Yes it would, but the beauty of an RO system in the first place is you can nearly purify very hard water.  You could get away without resin at 10ppm if it was a problem renewing it.

Peter

[steve.ternent]

There is a law called the law of diminishing returns. It would apply here, I think.

The cost of purifying water with an RO unit is about 60% product and 40% waste. Presumably the second RO would give similar results which would give a total of 36% product and 64% waste - and the tds of the waste from the second unit would only be about 20 ppm so you're throwing away very pure water.

Stick to DI, it's easier and probably cheaper in the end.

You never cease to win my admiration wally! 

Ever thought of teaching? I think you'd be good at it (maths that is)! 

[michael papworth]

A careful look at your idea shows that it really wouldn't work. In order to understand why not, we need to clear up a bit of thinking. It's common knowledge that the mains pressure affects the amount and purity of the product water. Well, that's not quite right. It's the pressure difference between the inlet and the outlet.

Putting a second RO unit would cause a back pressure which would then reduce the pressure difference across the first unit and hence reduce its efficiency. This would increase the tds reading and increase the amount of waste water. The second unit would then have the same low pressure difference problem.

I hope the diagram makes it clear.



The two pressure differences are probably going to be the same as the pressure difference across a single unit. Having two units in series is going to hugely decrease the efficiency of each unit and lead to a huge increase in the waste water.

Sorry. It sounded like a good idea, but in practice, it simply won't work.

[Xline Systems]

my very first system was a twin 40" ro. changed the two the first and second time. noticed a differance in the life of the ro's but couldnt justify shedding out for two ro's each time. so now i have just the one producing 2500ltrs a day.