An RO/DI system is a water filtration system that you keep at home to filter contaminants from your tap water, making it safe for use in your aquarium. The filtered fresh water is 99.9% pure and is used to mix saltwater and top-off your aquarium with freshwater lost to evaporation.

RO/DI: Reverse Osmosis Deionization System

Why Use An RO/DI System

Whether this is your first tank, or you have had tanks your entire life, all saltwater aquarium owners need to have an RO/DI system. While you can technically just buy water to use in your aquarium from the local fish store, having an RO/DI system at home has so many benefits, it's silly not to own one. Furthermore, the initial investment pays for itself with savings in under 12 months when compared to buying water from a local store.  

  • It's much easier and more convenient compared to alternative sources of water
  • It saves you money
  • You can be 100% confident the water is clean, free of contaminants and disease
  • Water is available on-demand in case of emergencies

How It Works

All RO/DI systems work the same way to filter your water down to 0 TDS - total dissolved solids. You connect a 1/4" diameter water line to your home's water supply which is controlled via valves. The water passes through a series of filters and along the way, water is split into a product water line and a wastewater line. There will be some rejected water you cannot use on your tank; for every 1 gallon of filtered RO/DI water, you will produce anywhere from 1-3 gallons of wastewater.

Product water is collected for use in your aquarium and the wastewater goes down the drain. When applicable, the wastewater can be used to water the lawn/garden or wash your car.  

RO/DI System Diagram

Water flows through the system as indicated by the dotted lines. The order in which the water passes through the filters is important for optimal filtration and longevity of the filters. 

Sediment Filter: Physically removes suspended particles from the water. Dirt, silt, clay, etc. 

Carbon Filter: Adsorbs dissolved contaminants such as chemicals, odors, some metals, and coloring agents.

RO Membrane: Thin-film composite membrane; the heart of your RO/DI system that removes 90-99% of the total impurities.

DI Filter: Ionically charged micro resin beads that remove any remaining contaminants after the RO membrane.

Read Article: How a Reverse Osmosis Deionization (RO/DI) System Works

Which One To Buy

Every single RO/DI system works using these same four basic filter stages but there are a variety of add-on accessories and upgrades you can choose to boost the performance of your RO/DI system. 

  • A booster pump increases water pressure should your home's water pressure not suffice.
  • An extra RO membrane increases water output and cuts wastewater in half
  • A pressure gauge and TDS meter allows you to monitor filter performance 
  • Additional filter stages can efficiently handle higher rates of production or target specific contaminants that are difficult to remove
  • Float valves can be used to automate the production and keep containers of RO/DI water full at all times
  • Drinking water upgrade kits allow you to keep a pressurized tank full of RO drinking water alongside producing RO/DI water for the aquarium

The beauty is, you can upgrade your basic 4 stage economy RO/DI system to include any or all of the aforementioned accessories should you need them. Just start with an affordable 4 stage RO/DI system and upgrade as necessary depending on your particular water quality and production needs.

The GPD or Gallons Per Day is how fast the system can make product water. For example, a 75 gallon per day RO/DI system can produce 75 total gallons of filtered RO/DI water in a 24-hour timeframe.  Choose according to how much water you use and how fast you want it.

Yes, production might seem surprisingly slow if you have never used an RO/DI system before and we always recommend choosing the higher production rates.  Notice the systems with 150 - 200 GPD production rates utilize two RO membranes which not only mean filtered water faster but also less wastewater.  

Learn More with BRStv: A Buyer's Guide to RO/DI Systems

How To Setup a BRS RO/DI System

We have made the BRS systems super easy to connect because they come pre-assembled with colored water lines so you can quickly connect the right tubes and produce RO/DI water on demand.

  1. Connect the RED line to your tap water source; always use the cold water line.
  2. The BLACK line is your wastewater which can be connected to a drain or collection container for recycling
  3. The BLUE line is your clean water that should be connected to a container for collection and use in your aquarium

Water Connections for RO/DI Systems

Tap Water Connections

There are a few different options for connecting to your tap water.  You can use the faucet diverter which just screws onto a standard sink faucet and has a valve that will divert water into the RO/DI system. This is a great setup for utility sinks or if you live in an apartment and just don't have the ability to make a more permanent connection.

A garden hose adapter screws onto your standard garden hose connection and works really well for connecting to the cold water line that feeds your clothes washer. Just get a garden hose WYE fitting with on/off valves and screw that onto the washer connection, then run one leg of the wye to your washer and the other to your RO/DI system.  

You can also make a more permanent connection to the water line under your sink which keeps the plumbing out of the way and really is not all that hard. The EZ angle stop adapter will easily thread into the standard plumbing of most modern homes or use a self-piercing saddle valve which is designed for direct connection to a copper pipe. 

Drain Line

You can use a drain saddle to permanently connect the wastewater line to your blackwater pipe under the sink. Alternatively, you can just shove the black line down into the drain in your sink or run it into the drainpipe by your washer.  If you decide to collect the water for recycling, just be sure the container is outside or somewhere that won't pose a risk if it overflows. It is easy to forget about and you will produce a lot of wastewater.  Some folks just run the line out into the garden or lawn when they are producing water then wrap things up for storage in between use.  

Of course, all BRS RO/DI systems come with detailed instructions but you can also review them here in our Education Center.  Just head over to the RO/DI Instructions category where we have some great articles about installing RO/DI systems and various upgrades.  

Push Connect Fittings

Push-Connect Fittings

Modern RO/DI systems use push-connect style fittings because they allow for a quick watertight connection. In order to remove the tubing from a push-connect fitting, you first push in on the plastic retaining ring or collar, then pull the tube out while holding that ring down on both sides. The ring must be pressed all the way down, up against the fitting, to release the tubing. It can be a little tricky at first but once you do it once, it is much easier to do moving forward. 

How To Use an RO/DI System

Before and after each use, you should flush the RO/DI system to rinse away any sediments that collect on the RO membrane.  

  1. Open the flush valve which is connected to the wastewater line. The black valve handle should rest parallel with the tubing when open. 
  2. Turn on the source water and let it flush for 1-2 minutes. All of the water will flush down the drain line. 
  3. Close the flush valve and you will start producing clean water.
  4. You can now collect water for use in your aquarium. Don't ever leave your RO/DI system running unmonitored to avoid water on the floor! 
  5. When you are done, open the flush valve and flush again for 1 minute before storage. 

Pro-Tips: When storing your RO/DI system it is important to not let the filters dry out. The best choice for long-term storage is to physically remove the filter cartridges and place them in a sealed Ziploc bag. This way the moisture is contained and the filters won't dry out.

In most circumstances, you will need your RO/DI system a couple of times per month if not more so a permanent mount and connection are the most convenient. Mounting the RO/DI system above your washer and dryer really works out nice and you can run the 1/4" product water line wherever you need it. You can easily run the water line 50-100ft or more without any problems and the tubing is small enough to run through the ceiling or discreetly tuck it into the corners as you would cable tv/ethernet wire.   

Building a water mixing station is also a great idea where you have your freshwater reservoir and saltwater mixing containers in a specific location next to the RO/DI unit.  You can produce all of your water at this single location and store all of the necessary pumps & supplies. There are a plethora of different ideas online, just search "saltwater mixing station".  

Learn More With BRStv: The Best Methods for Mixing Synthetic Seawater At Home