Reverse Osmosis: Explained

A Reverse Osmosis system, or RO system, is a popular water filtration method, widely known to create the most purified water of any filtration method. An RO system filters and softens the water through a series of stages. Below we explain the stages of this water treatment option, the maintenance required for it, and additional considerations to keep in mind for Reverse Osmosis systems. 

Five-Stage RO systems

There are two common types of RO systems: four-stage and five-stage. Each stage represents a filter within the system. North East installs five-stage units. While the science behind RO systems is quite technical, here’s a brief breakdown of each of the five stages:

  1. First particulate filter. This filter is used to get the larger sediments out of the water. This stage, often called “sediment” filtration, is used to protect the membrane and reduce the amount of particles it has to process.
  2. Second particulate filter. In our five-stage RO system, there are two particulate filters, which are intended to remove even more sediment from the water before it reaches the membrane. 
  3. Carbon pre-filter. This filter removes chlorine and other impurities that can cause foul-smelling, bad-tasting water and damage the RO membrane.
  4. The RO membrane. The semipermeable membrane stops roughly 99% of dissolved contaminants from passing, flushing them out the drain, and allows the water molecules to flow through.
  5. Carbon post-filter. After going through four stages of filters, RO water is often considered “flavorless”. Similarly to how most bottled water has minerals added to taste more familiar, this final filter is primarily there to help give a final “polish” to the water to help flavor the water. 

The treated water is not plumbed directly into your faucet. Instead, these systems come with a “glass filler” that’s added to your sink or countertop. Additionally, the RO water can be run to your icemaker for very high quality ice.

Required Maintenance

Based on manufacturer recommendations, RO system filters should be changed every six months, though this varies depending on use. The RO membrane, which lasts roughly two to four times longer than the filters, also requires changing periodically. 

If your water starts tasting different or your ice is extra cloudy, it may be time to change out the filters or get your system inspected.

Additional Considerations

As with any decision, there are a few additional points to consider when looking into an RO system:

  • Because the contaminants must be flushed out of the system, RO units can waste over three times as much water as it produces.
  • Water from an RO unit can damage a variety of metal piping, so only plastic tubing should be used to run any plumbing for the system.
  • Since RO systems waste so much water and take up a lot of space, a “whole house” system is not practical. While there are benefits to having purified water at all fixtures, such as your dishwasher, washing machine, and showers, a point-of-use RO system, or under the sink system, will only provide treated water to one or two fixtures.
  • RO units take up most of the space under a kitchen sink, a place often used for cleaning products. However, this may be more of a blessing in disguise, as storing chemicals under the sink can corrode piping and fixtures, such as garbage disposals, underneath.
  • RO systems are one of the biggest contributors to water loss insurance claims. The water is in a pressurized tank that also requires a drain. Although uncommon, if something goes wrong with the tank or drain it can flood your kitchen and cause extensive damage.

Still unsure whether a Reverse Osmosis system is right for you? Give North East Air Conditioning, Heating & Plumbing a call today to discuss your water treatment options and take the next step towards cleaner, better-tasting water.


Call: 210-658-0111