Build a 0-ppm water filtration system

completed 0 TDS water filter system with 2 prefilters, 2 RO systems, and 2 deionization filters

Bringing together multiple components to create a fast and efficient 0-ppm water filtration system, dubbed the Frank-n-Filter by the author. Photos courtesy of John Lowry

If you’ve worried about your water chemistry like I have, then you know how tricky it can be to get minerally consistent brewing water from any municipal supply. One possible upside to being on a municipal system is that some provide a mineral content report, which you can enter into your brewing software. But not all water departments provide that information and I don’t really trust the numbers I do get. You can buy water, but that is cumbersome and the cost adds up. You can send a sample of your tap or bottled brewing water to a lab to know the mineral content for 100% certainty. But this is an added cost and it’s only as reliable as your last sample and some municipal supplies change from month to month. Now I know brewing water doesn’t have to be perfect, but I’m tired of knowing little of the brewing water sourced from my municipal water supply.

We’ve had a reverse osmosis (RO) unit under our kitchen sink for years that’s produced great water but, due to leaking issues, was finally retired from that role. So, instantly my “brew-brain” kicked into thinking about how I could use this recently retired unit in my homebrewery . . . and not so much about how my family is going to get non-chalky ice cubes from the fridge in the foreseeable future. Don’t judge . . .you probably have a few of your own scores to boast about.

In researching what I needed for my brewing water filter (and yes, something for the family icemaker eventually) I learned about deionized (DI) or demineralized water and how scientists, aquarium owners, and car washes use it to filter their water. I also learned that during the RO membrane lifespan it removes ~99.9–85% of the solids from source water before replacement. My older RO membrane(s) showed 77 ppm (an 81.6% reduction in total dissolved solids or TDS), so they needed to be replaced. DI filter lifespans rely on receiving the cleanest water you can achieve prior to the deionization process.

There are a ton of choices out there, and you can get everything you need all in one setup if you’re buying new. “Reef”-type setups piqued my interest, as they were RO units with DI and carbon-block post filters. Since I already had the RO part of the unit I ordered a spot-free car rinse system to combine with it.

This unit consisted of two standard filter housings connected to each other and attached to a bracket, with 10-in. (25-cm) mixed-bed DI filter cartridges included. You can choose single-bed cartridges for each housing, which I’m doing next time to help minimize cost and maximize efficiency. If either filter’s plastic resin beads exhaust before the other, you don’t waste unused resin like with my mixed-bed resin. Some resin changes color as its filtering ability diminishes, making it easy to know when the resin needs to be replaced.

Now that I had everything, it was time to Frank-n-Filter this thing.

Tools and Materials

  • TDS meter
  • Plumber’s tape
  • Filter housing wrench
  • New or used RO unit (typically 3–5 stage filtration) with mounting bracket and flow control
  • Permeate pump (mine came with my RO unit because 60 PSI is needed for a membrane to function effectively)
  • Optional 2nd “matching RO membrane” (all membranes used have to match the flow control)
  • Dual-deionizing filter housings with mounting bracket
  • (2) 10-in. (25-cm) refillable resin filter cartridges and the resin you plan on using (mine came with full, refillable mixed-bed media cartridges)
  • Necessary plumbing connections