Reverse Osmosis FAQ

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Healthy drinking water provides a sense of security for you and your family knowing that potentially harmful contaminants have been significantly reduced! And a North Star reverse osmosis drinking water system in your home saves you money, over time, the system pays for itself!

ROs Improve Water Taste For Cooking And Beverages
  • Drinking Water, Coffee and Tea
  • Cooking and Baking
  • Ice Cubes
  • Baby Formula
  • Juice Concentrates and Mixed Beverages
  • Washing Produce
Enjoy The Convenience Of Clean, High-Quality Water Right From Your Tap!
  • Never buy bottled water again, delivers great tasting water instantly
  • No need to carry heavy bottles of water home from the store
  • Enjoy great tasting water on the go
Better Water Quality For The Whole House
  • Aquariums
  • House plants
  • Steam irons and ironing
  • Car batteries


These systems actually filter water then force it through a thin film, semi-permeable plastic membrane. Pressure from the home’s water system provides the pressure needed to push the water through the membrane. A small stream of water is used to flush the rejected impurities from the membrane surface and down the drain. Up to 99% of all dissolved solids are removed. Reverse Osmosis (RO) was first introduced to purify seawater to make it potable. It can remove virtually 90-99% of particles and ions. In general, reverse osmosis filtration restricts the flow of everything except water through a special type of membrane and allows oxygen to pass so product water doesn’t taste flat like boiled or distilled water. The RO filter is called a membrane filter because it works just like a natural membrane that surrounds a living cell. It is semi-permeable, allowing some molecules to go through the filter. ROFunction

  1. Water enters prefilter.  Sand, silt and other sediments are reduced.  Chlorine is also reduced.
  2. Water leaves prefilter and proceeds to the Reverse Osmosis Cartridge.
  3. Water enters the Reverse Osmosis membrane.  Dissolved solids are reduced.
  4. Processed water leaves the Reverse Osmosis Membrane and flows to the storage tank.
  5. Drain water with dissolved solids leaves the Reverse Osmosis membrane and flow to the drain.
  6. Faucet is activated.
  7. Processed water leaves the storage tank and flows to the postfilter, where it is filtered to ensure fresh taste.
  8. Water flows to the Reverse Osmosis faucet.
How The RO Membrane Works

The semi-permeable membrane is wrapped around a hollow cylindrical core. Feed water flows along the surface of the membrane. A flow restrictor limits the feed water flow rate creating back pressure that forces some of the water through the semi-permeable membrane. Once inside the membrane, the filtered product water follows the inside of the envelope to the core. The water that doesn’t pass through sweeps the filtered dirt, particles and debris from the membrane surface and carries the residue down the drain.

Feed Water

Feed water is the key to the quality and production of the reverse osmosis filtration system. The following specifications should always be met:

  • Feed water: PSI 40 – 125 PSI
  • Feed water Temperature: 40 – 100 (F)
  • Max. Total Dissolved Solids (TDS): 2000 ppm
  • Max. Hardness: 10 gpg
  • Max. Iron, Hydrogen Sulfide, Manganese: 0 ppm
  • pH limits: 4 – 10
  • Chlorine allowable:2 ppm
The Prefilter

The prefilter is a replaceable activated carbon sediment filter. The filter is necessary to remove sediment that would otherwise clog the RO membrane and chlorine that would destroy the membrane. After a time, the prefilter begins to plug and water cannot get through it as fast which eventually slows water production. The prefilter will remove:

  • Up to 5 microns of sediment (dirt, sand, silt, etc.)
  • 2 ppm chlorine taste and odor

Prefilters should generally be changed every 6 months depending on water usage and the chlorine levels in the water.

The Postfilter

The activated carbon postfilter polishes of the product water. It will remove most unpleasant tastes and odors and sediment. The water passes through this final filtering process immediately before going to the faucet. Postfilters should generally be changed every 6 months depending on water usage and the chlorine levels in the water.

Automatic Shutoff

To conserve water, the drinking system has an automatic shutoff that functions by pressure. The automatic shutoff consists of 2 diaphragms and a plunger. The plunger moves up or down in the housing based upon diaphragm pressures. The lower diaphragm pushes the plunger up allowing feed water to flow through the inlet/outlet port until the storage area pressure exceeds one half the inlet pressure. At this point, the storage area pressure on the upper diaphragm is great enough to push the plunger down stopping the flow of feed water. Flow will not start again until the storage area pressure drops because of water withdrawal at the faucet.

The RO Membrane Cartridge

The RO cartridge is a tightly wound semi-permeable membrane. When water is forced through the membrane, it flows only one way down into the cartridge. This high quality product water is directed into the storage area or out to the faucet. The membrane has 2 O-rings on one end that fits into the check valve. Rejected water flushes the membrane surface and carries the dissolved solids to the drain.