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Old 08-05-2008, 09:51 PM   #1
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DI unit

Hi everybody!!!Always when i ask question i think probably that is the last one.Couple days and I'm here again.R/o-DI units producing a lot of waste water.<it is kind of expencive where i live>My LFS store sells DI unts<they make them>.You do not have waste water at all.I realize that is not as pure as R/O but is probably a lot better then tap witch I'm using right now.It has three stage of filtration.What do You guys think?Is it worth it 300 dolars?Remember there is no waste water!!
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Old 08-05-2008, 09:57 PM   #2
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You can get a RO/DI unit for about 100 dollars on ebay and some other sites. An RO unit would be even cheaper. I`ve never had a DI unit but it would take alot of waste water to equal the extra 200 to 250 dollars.JMO
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Old 08-06-2008, 01:01 AM   #3
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$300 for just a DI unit??? That's robbery. Look here...

The Filter Guys

I run a DI unit, no RO. The output is as pure as pure gets and is probably purer than just RO by itself. RO/DI together though will give you pure water also.

I run the water first through a Kold-Steril unit (bad purchase... long story) that takes out heavy metals, big junk, and the chlorine. It then passes through a dual cannister DI unit from the fine gentlemen at the link above. I have a flow meter/valve inline so I can dial in the exact gallons/hour I want flowing through it. Even at flow rates of 60 gallons/hour my 80ppm TDS tap water turns into 0.0ppm TDS pure water. No waste.

Is it for everyone? No. It's expensive. I burn through a DI resin refill about every 5-6 weeks, at around $10-12 a pop. But for me, the ability to have DI water on demand, with no waste, is worth it. Just a personal choice.

Melosu is right though... if you calculate out how many $$ you are spending on that waste water (just assume you throw out 4 gallons for every 1 you make) it's really not that much money and you'd be hard pressed to justify the extra expense of straight DI just on money.

But again... $300 for a DI setup is just plain ridiculous - even if it comes with carbon prefilters, etc.
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Old 08-06-2008, 08:01 AM   #4
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I wasnt dogging DI units Kurt. I`ve never used one. I was giving my advice on RO and RO/DI units. Thanks for the info on the DI.
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Old 08-06-2008, 11:53 AM   #5
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I wasnt dogging DI units Kurt. I`ve never used one. I was giving my advice on RO and RO/DI units. Thanks for the info on the DI.
I know you weren't taking issue with straight DI - but you're right... if you total up the actual cost of the waste water from an RO unit, it's a LOT fewer $$ than you'd think it would be. Even with "expensive" water, it's still relatively cheap - money wise. Plus many folks store the waste water and use it for other uses, so it's not really wasted.

I was just mostly wanting to point out to artur that DI water is just as pure as RO/DI, and probably MORE pure than just RO, because it strips EVERYTHING out. But it comes at a cost. And I also wanted to let him know that if someone was trying to sell them a straight DI unit for $300, they should immediately RUN AWAY from that store!
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Old 08-06-2008, 12:00 PM   #6
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I was under the impression that DI units produced no waste water due to the way they are designed. RO units on the other hand can have 3 parts waste water : 1 part nearly pure water.
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Old 08-06-2008, 12:35 PM   #7
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I was under the impression that DI units produced no waste water due to the way they are designed. RO units on the other hand can have 3 parts waste water : 1 part nearly pure water.
I have a RO/DI unit it has 1 waste water line. I drain it into my Washing machine drain so I don't really see how much it is wasting. There is a line for dispensing RO water for drinking(98% pure) and another line for the RO/DI (99.99% pure) water I use to fill a garbage can full for the aquarium. I spent $195 shipped for my unit from MelevsReef It produces well over 100gpd. I was spending like $1.25 a gallon at the LFS for pure water. Thats 156 gallons to = the cost of the unit about 10 water changes. so in about 3months it paid for itself. I also saw no affect on my Water bill at all maybe like $4 or something for a 2month period I also don't use it very much since I only have a 46g tank I am sure if you had a 500gallon display it would have a bigger impact. The amount of water it takes to fill my 32 gallon container of RO/DI including waste water is only about the same as taking 6 showers. I have a family of 4 so that is an easy amount of water to use. Just a little food for thought.
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Old 08-06-2008, 01:49 PM   #8
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I was under the impression that DI units produced no waste water due to the way they are designed. RO units on the other hand can have 3 parts waste water : 1 part nearly pure water.
Well... yes and no. Comparing just RO to just DI is like comparing apples and fish - they're just plain different.

RO "filters" water in a manner that not all the water makes it through the RO membrane. That water is bypassed and discharged as waste water. The good water can still have some bad stuff in it, even though it has passed through the membrane. But that amount will be very very small.

DI resins "filter" the water by stripping the bad stuff off the water as the water flows through the resin. There is no waste because there is no bypass. Flow the water slow enough through the resin, and you'll strip everything off.

That's why you normally have a DI stage after the RO membrane. The RO membrane will take out 95-99% of the bad stuff, and then the DI resin strips out the remaining stuff to get you pure water. And since the RO membrane is doing most of the work, your DI resin will last for quite a while - unlike just using DI by itself.
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Old 08-06-2008, 01:51 PM   #9
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Thanks Kurt. Great explanation
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