How To Select, Install Reverse Osmosis System
Enjoy Limitless Pure Filtered Drinking Water For Pennies a Gallon
Apr 22, 2009
Reverse osmosis home filtration systems provide large volumes of pure, clean, color- and odor-free water for people, pets and plants. A "hard wired" RO hyperfiltration unit is a convenience easily within reach of the average DIYer.
RO System Basics
A domestic DIY-ready RO system typically consists of several components, often sold as a kit:
- Filter Array—four to six factory-connected filters mounted on a hangable metal housing. Higher cost systems employ more filters and deliver slightly cleaner water.
- Holding tank—a 3 to 6 gallon capacity pressurized vessel that stores filtered water ready to flow to a sink- or counter-mounted faucet. Until direct flow systems hit the market recently, the RO process has been too slow to instantly provide a gallon or two of filtered water, hence the need for a tank. Tankless direct flow units are pricier.
- Faucet
- Automatic shutoff valve; hoses to connect the filter array to feed water and to the faucet, and for waste discharge
- Needle-piercing saddle, or standard ball, feed water valve,
Water flows through the filters and is successively cleaned in “stages” as follows:
- Stage 1 Prefilter, 1 - 5 micron—removes sediment, suspended rust and sand.
- Stage 2 Prefilter, granular activated carbon (GAC) 1 to 5 micron—removes most chlorine, organic chemicals, taste, color and odor.
- Stage 3 Prefilter, activated carbon block, 1 to 5 micron—further removes chemical entities Stage 2 filter missed.
- Stage 4 Filter, osmotic membrane—the workhorse filter that gives the system its name. Removes 92% to 98% of all remaining chemicals and dissolved solids in tap water.
- Stage 5 Postfilter, deionization (DI)—removes remaining dissolved solids. Premium systems have 2 of these when ultra pure water is needed for aquariums, hydroponics and laboratories.
Selecting a System: How Large?
Choose an RO system with a filtration capacity sufficient to meet family needs. A unit that generates 3 GPH (gallons per hour) has about the same capacity as one rated at 75 GPD (gallons per day), and is large enough for many households.
Pre-Installation Considerations
- Many RO systems require a minimum water pressure of 40 psi. Booster pumps are available if pressure is a problem.
- Consider a whole-house filter, ahead of the RO unit, if incoming municipal or well water is unusually turbid.
- Choose a spot for the filter array (approximately 18” H x 18” W x 8” D) that’s easy to access, since the unit needs to be serviced twice a year. If the undersink area is too small to stand or hang the array, consider a basement, utility room, etc.
- Select a location for the holding tank (approximately 18” H x 12” W x 12” D). It can be spotted anywhere up to 30 feet away from the filter unit.
- If there’s no available kitchen sink-top hole to install the added clean water faucet, replace the kitchen faucet with a pullout spray head model to free up the sprayer hole, or drill a new one in the countertop or sink. Careful: porcelain, marble, granite and some composites may shatter or crack unless a specialty bit and proper technique are used.
- Supplies needed: common hand tools and Teflon thread paste.
Install the RO System
- Install the faucet and place the storage tank in desired location.
- Connect the feed water valve to a cold (not hot!) water line.
- Hang or stand the filter array and place a drip pan beneath it.
- Run a water discharge line from the filter array to a utility sink, or into a drainpipe above the trap via a saddle.
- Connect all hoses and fittings.
Maintaining RO Systems
Except for the osmotic membrane, which lasts two to three years, change out filters approximately every 6 months or 6,000 gallons.
Cost of RO Water
An average 75 GPD system and replacement filters to last 5 years run about $300 to $400. Altogether, including equipment amortization and water (RO systems “waste” 3 to 4 gallons for each gallon of purified water), it costs 8 – 15 cents per drinkable gallon.
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