# RO Water - Whats readings?



## mlgt (13 Feb 2012)

Generally RO water is of a set level reading.

But wondered if the location of where you are makes a difference at all? 

Im interested, well for some time to get myself a RO unit, but think I will take the plunge next month.

I dont intend to get a big output, but this will aid the Rena 350l tank as pretty much all my fish are Asian type which would be healthier with a lower ph, gh, tda etc. 

Finding out that my new flat does not have a water meter makes this purchase a no brainer 

Wanted to know readings purely from its source, if you have readings with tap water will be interesting too 

Thoughs and comments welcome.


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## dw1305 (14 Feb 2012)

Hi all,
It really depends upon the set-up, ideally you want to start with fairly soft water, but you can make de-ionised water from sea water with the right kit. Your water will be quite hard, so with apologies for the cross-post, but have a look at this: <http://www.plecoplanet.com/forum/showthread.php?t=11157>

cheers Darrel


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## mlgt (14 Feb 2012)

Thanks for the link Darrel 

A fewquestions regarding wastage from the ro unit. I know there are other version of RO unit with DI and there is no waste.
However is there any use of the waste ro water? I read that use it to remineralise the ro water and some would cut with tap water etc.

But is there any actual harm of keeping this waste? Im not on a water meter so it doesnt bother me, but trying to be more environmentally friendly and reading from that page that bacteria wil grow in the water due to the chemicals stripped from the water.

How would one keep this at bay? Due to the fact that ro water takes a certain amount of time to produce.
I was intending to keep the waste water to water plants such as orchids and if I can save enough wash my car with it.

Also is waste ro water dangerous to drink? Will it do any harm to use it to wash with? Just a fwe questions that popped in my mind


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## Skatersav (14 Feb 2012)

I've got an RO unit.  I worried about the environmental impact of so much water wastage and still do to an extent.  
However, I think the environmental impact is low.  Water run off in itself is not really damaging - it's completely natural.  What is a problem is that re-coursing of water away from a natural habitat for the purposes of human consumption - limiting this, by limiting wastage, is no doubt a good thing.  And, on this basis, RO units cannot be considered positive for the environment.  On the other hand, I don't see the aquarium trade's most significant negative externality as being RO units.

The waste water shouldn't be bad to drink.  It will have a higher level of mineralisation than normal tap water, but only by a tiny amount.  When you get your RO unit and see how much RO water is produced from a fast running tap, you'll understand.  If the tap water was safe to drink before, then it will be afterwards.

In terms of what else to use the waste water for - well, if you are planning on using RO water for a 350litre tank, you are going to have a LOT of waste water.  It takes me about 8 hours to fill up a 25 litre container with RO water and I normally fill up around 2 a week to do my water change - I cut it with normal tap water so that I can do a ~50% change in a 300litre tank.  I wouldn't be surprised if an RO unit ran at 50:1 waste to RO water.  Basically, you would have to have a very substantial storage capacity to make use of a material proportion of the waste water.  I guess you could bathe in it if you don't mind cold water.  Or you could wash a car with it if you have a big container to store it in (think very big).  Or if you have another tank in which the inhabitants like harder water, maybe use it for that.


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## dw1305 (14 Feb 2012)

Hi all,
The amount of rejected water is controlled by several factors, the main one is water pressure, the higher the pressure the greater the amount of water forced through the semi-permeable membrane. In theory you should be able to reach a point were you have no rejected water by increasing the pressure, for this reason a booster pump is a good idea, unless you have a really high rising main water pressure. Temperature is also a factor, cold water gives a smaller yield of RO than warmer water.

The problems come with membrane scaling etc which mean that realistically you would expect to have to reject about 3 litres of tap water for every 1 litre of RO produced, even in the best systems.

There is nothing wrong with the rejected water, it has been through the carbon and sediment filters, so you can drink   it, shower in it etc. It won't have any chlorine left so things may grow in it if you store it, but I wouldn't worry too much unless you want to drink it.

It will have a higher TDS than your tap, so I wouldn't water the Orchids with it (stick to rain water), but fine for tomatoes, lawns etc. 

cheers Darrel


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## mlgt (14 Feb 2012)

Well currently I tend to do water changes around 2-3 weeks depending on feeding and the smell I get from the tank.
Since it is a low tech tank and full of plants and fish I believe the balance is actually quite good.
It is filtered by 2 jbl e1500 filters and I only feed once a day. Every third day I will put frozen bloodworm/brineshrimp and feed the clean up crew blanched veg or algae wafers sparingly.

I would say the 350l along with substrate and plants etc would only realistically be around 300l and I tend to change around 150l or thereabouts each time. 

I would assume I would save around 100l+ of RO water and cut some of the waste with tap water to provide minerals. 
However due to my fish not being used to RO water I would need to introduce this slowly and reckon 50l at a time.

Sadly I dont have a big storage container so therefore it will be stored in 25l containers going forward but I do have a spare room for this.

For the waste I could always install a water butt to collect this water, but how fast do you find RO waste water runs compared to pure RO water ?


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