View Full Version : Making an RO/DI Unit

12/11/2007, 06:59 PM
Anyone every made a nice size commercial RO/DI filter? I keep hearing about them being made...

Plans? Or just DIY for real?

I'm roughly looking for about a 800-1000 gallons per day and may need to upgrade to more then that once I get some expansion on my greenhouse.

12/11/2007, 07:12 PM
A system that large is more than most DIYers have knowledge to build. You will either need several parallel membranes fed by a fairly large booster pump a few high volume membranes in series. In most cases, high capacity membranes have a lower rejection and your DI usage and waste water will be fairly high.

I would contact reputable vendors and take a look at their setups. It is one thing to make 100 gallons a week at 4:1 rejection to product, it is another to make 1000 gallons a day at that ratio. Likewise resin usage at 1000 gallons per day at 95% rejection will get costly.

12/11/2007, 07:21 PM
I agree, but look at Redox's system...made by one of his buds.

I am not aware how much DI resin he uses though...but that's a good point, thanks for addressing that Bean.

I found a 700 GPD for like 399.99, not as bad as 2,000.00 dollar ones that are only making 300 more gallons.

12/11/2007, 07:42 PM
Just be sure you are comparing apples to apples. In this case rejection and waste are the key points.

12/11/2007, 08:00 PM
Thanks Bean.

12/11/2007, 09:59 PM
NP.... have fun and do your research!

12/12/2007, 07:55 AM
Not to mention the initial cost of all of those membranes. I think you are better off looking into one of the commercial high volume units.

12/12/2007, 09:46 AM
That's not the issue.

It would be cheaper making your own if you can tune it to have less waste water anduse the waste water to do something with, such as for filling your swimming pool.

I found a unit I think I'm going to buy, and add a DI canister to it. Total cost around 450.00 for a 700gpd unit with a tds meter.

12/14/2007, 12:13 AM
Are you going with The Merlin from airwaterice

12/14/2007, 08:04 AM
Thought about it...

But I'm not going to buy it from AWI I don't think...although I'll check their prices as well.

12/14/2007, 11:10 PM
I use a Merlin at work ... it seems to do real well. Reads 0 TDS coming right out of the RO only.

It's been in use for at least 6 months. We use it on a 1000 gal reservoir. No problems as of yet.

12/15/2007, 08:41 AM
Ok so it is a good unit...

It almost sounded too good to be true, about some of the features.

12/15/2007, 09:02 AM
Well one feature that may be over exaggerated is where it says that you don't even need a bladder tank. I see how fast it comes out (don’t recall exactly how fast) but if you're using it for for a faucet ONLY then you shouldn’t need a bladder tank. It's larger than a conventional unit and all the hoses are larger so upon startup you do get a good gush of water because it's all pressurized.

I do not know anything about the membranes accept that they are big :) so I can not say much about their quality. Their stats may be accurate, but they are likely based on 'ideal parameters'.

I just didn’t like the fact that it is so unitized. It’s like one solid mass and there’s nothing to tinker with. I do not know if you can add another membrane or not. If for any reason that the ASO valve takes a dump I don’t know if you can change it out. Everything seems to be embedded in plastic. The only thing you can remove is the hoses, filter elements and the membrane.

12/15/2007, 10:37 AM
Keep in mind the rejection rating or efficiency of the Merlin is not as high as the 75 GPD units. You are comparing 96-98% units to a high production 90-93% unit. DI life will be much much less.

12/15/2007, 01:21 PM
Well I don't know what I'm going to do then.