Water Filter Guides
Whole House Reverse Osmosis Systems

Whole House Reverse Osmosis Systems

Whole House Reverse Osmosis Systems

Reverse osmosis systems use semi-permeable film membranes to separate and remove dissolved solids, organic material, pyrogens, submicron colloidal matter, viruses, and bacteria from water.  Feed water is delivered under pressure to the membranes where reverse osmosis takes place.  Water permeates the minute pores of the membrane and is delivered as purified product water.  The impurities in the water do not pass through the membrane, and are instead concentrated in the reject stream that is flushed to the drain.

While ordinary filters use a screen to separate particles from water streams, a reverse osmosis system uses a semi-permeable membrane to separate a high percentage of dissolved molecules.  Only certain types of molecules, like water, can pass through the membrane.  Other molecules, like salts, do not pass through the membrane and are left behind. A semi-permeable membrane is made of thin, multi-layered sheets with microscopic pores that let water pass through while acting as a barrier to stop dissolved particles like salt.

Under-Sink Reverse Osmosis Systems

Whole House Reverse Osmosis Systems
Under-Sink Reverse Osmosis Systems

Under-sink reverse osmosis systems are used to purify water of sodium, total dissolved solids, metals, and other inorganic impurities in water.  They also include carbon filters which remove chlorine tastes and odors, along with other organic compounds such as pesticides and herbicides.

A reverse osmosis system that makes claims to remove contaminants that affect health (such as lead) will be certified by a third-party certification organization such as NSF, U.L, or WQA. The under-sink reverse osmosis (or “RO”) systems are sized in their output in gallons or liters per hour or per day.

A typical home system will produce between 25 and 50 gallons per day for instance.

Under-sink RO systems use a separate faucet to dispense the purified water. Purified water can be supplied to icemakers and on-door water dispensers if the production of the RO is sufficient and there is a large enough pure water holding tank.

Whole House Reverse Osmosis Systems

In some cases, the total dissolved solids are so high (typically over 1000 mg/L) that it is necessary to remove them for all the household water use. Advantages of whole-house reverse osmosis systems are that your water will be of drinking quality throughout the home, and not corrosive to piping and fixtures.   If the piping in the home is copper, the final stage of the whole house RO system will include a calcite neutralizer that adds some minerals back into the water after the RO system has purified the water of total dissolved solids. This type of RO system has its own booster pump to boost pressure from the line pressure of 50 or 60 PSI up to 200 PSI for TDS of 2000 to 3000 mg/L, and up to 400 to 900 for brackish and seawater applications.

Common features include pressure gauges, a control panel for wiring and controlling the RO system, and flow meters that show the pure water flow rate, waste water flow rate, and recycled water flow rate.  Many RO systems will also include TDS meters and flow sensors to track water quality and trip an alarm should the water quality deviate from standard settings or the RO system require service. Typical whole house RO systems have six main requirements: Adequate pre-treatment to remove iron, manganese and solids Disinfection to remove bacteria that may foul the RO membranes Anti-scalant control which includes either a water softener or an anti-scalant injection system using a non-toxic chemical Adequate pressure and flow before the RO system Neutralizer for pH and minerals to make the water non-corrosive Storage tank with booster pump to hold the purified water

Typical Whole House RO System Using the Well Pump Directly

This type can purify the water directly from the well using the well submersible pump to supply the feed water to the pre-treatment and the RO system.  The water fills a holding tank. In this type of RO system, the untreated well water is filtered for iron and manganese with a Pro-OX (or greensand etc) iron water filter, then a sediment backwash filter for turbidity reduction.  If the water contains high levels of hardness over 3 – 5 grains per gallon, a water softener or anti-scalant injection system is used prior to the RO system. The water is purified of dissolved solids by the reverse osmosis system and then flows through a calcite neutralizer, which adds a small amount of calcium back into the water to prevent corrosion of household piping.  If the water is to be used for irrigation only, or in a bottling plant, often no calcium is added. This design can be used for waters high in iron, manganese, and total dissolved solids.

Typical Whole House and Commercial RO System with Chlorinator

Whole House Reverse Osmosis Systems
RO System with Chlorinator

In this type of RO system, water is injected with chlorine (optional contact tank not shown) killing bacteria and oxidizing iron and manganese.  The water is filtered for iron and manganese with a Pro-OX (or greensand etc) iron filter, then a carbon filter, then water softener (if water contains hardness). The water is purified of dissolved solids by the reverse osmosis system and then flows through a calcite neutralizer, which adds a small amount of calcium back into the water to prevent corrosion of household piping.  If the water is to be used for irrigation only, or in a bottling plant, often no calcium is added. This design can be used for waters high in iron, manganese, odors, TDS, arsenic and other contaminants.

Daniel Vincen

Mr. Daniel Daniel is a licensed professional geologist and soil scientist with over 25 years experience in applied earth and environmental sciences. Targeted outreach to private well owners and city water users in Pennsylvania, but we assist private water systems worldwide.

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