What to look for in an RO filter?

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Jan 21, 2019
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Looking to get an RO filter to make my own RO. What should I look for? Are there certain types of filters I should be using? Here is a link to my water quality report in my city water report TDS is 432. We have relatively high sulfates at 175 ppm.

I want to keep it cheap as this will only be used for my homebrew and not the rest of the house.

Found a used one of these Rainfresh RO450 for $50, would that be good? Or is something else better?

If I do get an RO Filter what do I assume for the water chemistry of the filtered RO water? 0 for everything?

The alternative is to buy RO water for $5 per 5 gallons.
I bought and have been using AquaSauna, they are in Texas, USA. They have a "water for life" program that is outstanding as is their C.S.
The units are efficient with water consumption for industry standards. They are the only ones I could find that would also remove Fluoride and HEX6. IT also comes with a re-mineralizer.
If you visit the site sign up for email, get 50% off and grab the water for life program. My filter prices are locked in to years ago prices and when ever I call with a warranty issue it is handled.
You get what you pay for. I use it for all, the only thing is the recovery or bladder, you will find this true of most. The bladder holds about 2.25 Gal so you will need to think ahead and start to reserve your H20 for Brew day. I have #6 1gal jugs and a couple days before I start to collect, R.O re-mineralized water for some of the best beer around.
The Units infront of stores, have old filters that have micro organisms in them akin to a bathroom air dryer that spends it's time sucking in **** air in the restroom to blow on your hands to dry them.
This company makes a portable RO system, failed the kickstarter, but had enough external backers to get off the ground. looks interesting, but I have not found many users to get a solid review. A bit pricey too.

I had been thinking of just using a under sink RO system, but modifying it to work in the garage. I have seen some under $300 on amazon. Figured I would just need to patch into a water line and let it run into a 5 gal jug/bucket.
To be fair, a RO system is opening a can of worms so get ready.

It's easy to get nice pure water with any RO system after it have just been unboxed, the challenge is to keep the membranes functional along time. If water is relatively concentrated on dissolved solids, some of them can precipitate within the membranes as water permeates through them. Enough precipitation renders the membranes useless and they have to be replaced, which is costly.

You can download a free version of GE Winflows software and input your water test report to see whether there is a risk of precipitation or not. Particular components to watch for are hardness ions (calcium and magnesium) and silica. If you already have a water softener, feed the RO membrane with softened water and it will work better.

Pay attention to the rejection rate of the membrane (the amount of brine water is produced per liter of deionized water). Some systems may produce and equal amount of rejection water for treated water, so plan your water consumption accordingly. Also check the output flow, since some of them may be slow and require to start the system with hours of anticipation to have enough for a brew.
What size batch size are you brewing right now?

I would say the cheapest and simplest way to go is a 25-50 GPD system, and add a large storage tank so that you can draw off all your water that you need, and don't have to worry about the membrane filtering the water on demand.

I will say that your TDS seems really high to me, so you may need to also plan on replacing your filters more often if they get saturated.

I went with an RO-Pure setup that I bought from Costco on sale, and added an 11 gallon tank in parallel with the small one that came with the system (just some extra rigid tubing and john guest fittings). Keep in mind that with these common RO systems, the storage tanks don't actually store their given capacity, there is a bladder in there that takes up space. If you needed somewhere around 10 gallons of water, I'd probably get a tank in the 20 gallon size range.

Also, if you are mashing with the RO water, make sure you add back in brewing salts so that you can get your mash pH in the right range as well as your flavor profile for your particular beer.
Realize that there is very little cost difference between a 50 gpd system, and a 100 gpd system, at least in our lineup. We always suggest the 100 gpd for home brewers.

Given that the time to produce enough RO water for brewing is still in the 'hours' range, its somewhat silly to think that employing a 100 gpd membrane is going to be 'better' than a 50 gpd membrane. They're both going to take a good long time and a brewer will be waiting a long time to collect enough water. Setting up a good storage vessel with a reliable shut-off mechanism is going to be a more economical and pleasant experience for a typical homebrewer.

A good bet is to employ a high quality membrane that has decent production and delivers excellent dissolved solids rejection. Based on those criteria, I've settled on the Filmtec BW-1810-75 membrane as a go-to for my system. The BW designation indicates that its optimized for brackish water and improves TDS rejection.

Another confounding consideration for high capacity membrane use arises when your source water has chloramines in it. Then a high capacity membrane can actually result in too high of a flow rate through the carbon block and chloramine removal can be incomplete. If you have a proper storage vessel and shut-off mechanism, low to moderate capacity membranes are more likely to provide better service life. Bigger is not always better.
I went with the 100 gpd system from Buckeye and added a 14 gal pressure tank. I have a line straight to the brewery and two lines going to the kitchen. The water goes through a whole house filter and a water softener before the RO. I can fill while I'm setting up and I'll have 8-9 gallons in less than a half hour. I haven't actually timed it. Get 3/8" lines if you're plumbing a distance from the RO system. I did get the pressure tank off Amazon, full disclosure. It was free shipping. Other than that, definitely give Russ at Buckeye a call.
A good bet is to employ a high quality membrane that has decent production and delivers excellent dissolved solids rejection. Based on those criteria, I've settled on the Filmtec BW-1810-75 membrane as a go-to for my system.

That membrane (our best seller, BTW) is rated at 99% rejection.
A number of years ago, the best Filmtec had to offer at 100 gpd was the TW30-1812-100 rated at only 90% rejection.

Then Filmtec introduced the TW30-1812-100HR with a rejection rate of 98%. This is the only 100 gpd membrane we've sold since it became available.

Buyer beware... there are still vendors out there selling the old 90% rejection elements.