Reverse Osmosis Systems

Homewater - Reverse Osmosis Systems

What Is a Reverse Osmosis System

A reverse osmosis (RO) system is a proven water purification technology that helps remove chlorine and other unwanted impurities from water. During the reverse osmosis process, water pressure pushes water through a semi-permeable membrane. On one side of the membrane, contaminants are blocked, allowing only water molecules to flow out into the other side. While osmosis occurs in nature, reverse osmosis was not developed until the 1940s, as scientists searched for ways to desalinate seawater. Today’s reverse osmosis systems implement advanced technology and more refined membranes for a variety of at-home and industrial applications. [1]

How Does a Reverse Osmosis System Work

Chances are you have seen and experienced the process of osmosis. Ever gotten out of the tub and had wrinkly fingertips? That is osmosis at work. It occurs anytime water moves from a lower concentration to a higher one by passing through a permeable membrane. This occurs naturally to help achieve equalization between two liquids. So when your fingers get wrinkly in the bath, it is in part due to osmosis. When the freshwater from the bath passes through the cell membranes inside your fingers, it is nature’s way of trying to balance out the saltiness inside the cell compared to the freshwater in the bath. As a result, swollen fingertips get infused with the bathwater, lowering the cell’s salt concentration. Another example of this can be found in snails’ reaction to salt. When cells inside a snails’ body encounter a high concentration of salt, the liquid literally flows out their body towards a higher salt concentration–effectively killing the snail in its tracks. [2] Reverse osmosis takes inspiration from these natural occurrences but reverses the direction of the process by using pressure. So, instead of water or liquid flowing from a low concentration through a membrane to a higher concentration, water pressure is used to push the water from high to low concentrations. For example, most water, even after it leaves a treatment facility, has all kinds of minerals, chemicals, and metals left in it. Reverse osmosis takes this kind of water, which has a high concentration of other molecules floating around, and pushes it through a permeable membrane so that the only thing left is pure H2O with zero total dissolved solids. The RO system then dumps out the remaining impurities or leaves them trapped in a filter, so you don’t drink it. Put simply, an RO water filtration system works by taking out the bad stuff from your water–leaving behind only pure, great-tasting drinking water. In-home RO systems usually employ some variation of the following steps.

Step 1: Pre-Filter or Sediment Filter

Typically some kind of pre-filter is used with reverse osmosis systems to protect the integrity of the RO membrane. The pre-filter removes large sediment from the water before passing the water through the next step. This pre-filter is especially critical if your water is hard and contains lots of minerals like calcium and magnesium that will quickly clog up your RO filter.

Step 2: Reverse Osmosis Filter

Once larger particles are removed from the water, it is ready to pass through the osmosis membrane. Water is forced through the semi-permeable membrane using pressure. The membrane is usually made of a synthetic material that is constructed to allow water molecules to flow through but stops things like chlorine, bacteria, and viruses from passing through. The remaining wastewater with contaminants gets routed out to a drain.

Step 3: Activated Carbon Filter

After the second step, your water should be safe to drink. However, many reverse osmosis systems, especially whole home filters, will utilize a third filter before sending it on to your taps or uses a permeate pump to direct water to a storage tank. This additional filter typically runs the water through an activated carbon filter that can absorb any remaining impurities that may have slipped through the previous two filtration steps. The result is water, which is 99% free of any contaminants or impurities.

How Does an RO Membrane Work?

When working correctly, RO membranes allow water molecules to pass through, while preventing other contaminants from moving through the filtration process. RO membranes accomplish this through microscopic pores. These pores are large enough for water molecules to pass through but small enough to trap anything else. These pores are extremely tiny and are usually 0.0001 microns in size. These membranes are made using synthetic materials like cellulose acetate or polysulfone. [3]

Should I Switch to an RO System

There are many factors that go into selecting the right water filtration system for your home, including your home’s water source, budget, and other water needs. When deciding, you may also want to consider some distinct advantages that installing an RO system provides, including: Cost savings compared to bottled water Small footprint that won’t take up too much space in your home Lower energy costs thanks to energy-efficient systems

Reverse Osmosis Water Benefits

One of the best benefits of selecting a reverse osmosis water filter for your home is the great-tasting water you and your family can enjoy. Reverse osmosis filters reliably remove the things that can make your water smell or taste bad. If you are using water from a well or other unreliable tap water source, then a reverse osmosis water filter can help ensure your water is always safe to drink, cook with, or bathe in. According to the Center for Disease Control and Prevention (CDC), an RO filter system can remove or reduce harmful contaminants, which include: [4]
  • Cryptosporidium
  • Giardia
  • Campylobacter
  • Salmonella
  • Shigella
  • E. coli
  • Enteric
  • Hepatitis A
  • Norovirus
  • Rotavirus
  • Lead
  • Arsenic
  • Fluoride

How Much Maintenance Does an RO System Require

Once an RO system has been properly installed, it requires very little maintenance. The main thing which will require upkeep is the replacement of the pre-filters and the activated carbon filters. Most RO system filters can be replaced on your own by temporarily shutting off the water supply, unscrewing the canister, pulling the older filter out, and inserting the new one in. The reverse osmosis filter itself can run for years with no required maintenance. The RO membranes can last up to five years, and will usually need to be replaced after that. Replacement of these filters will not cost much when spread out over a year, typically less than a dollar a day, depending on the exact filter type, size, and complexity of your system.

How Much Does a Reverse Osmosis System Cost?

Reverse osmosis systems come in a variety of sizes to handle different amounts of water and applications. Two of the most common forms of RO water filtration systems for your home include under the sink water filtration systems and whole home water filtration systems. Under sink systems only filter the water for a single sink in your kitchen or bathroom, and whole-home reverse osmosis systems will filter out gallons of water at a time for your entire home. Under-sink filters can cost between $150 and $250 on the low end but can go up to $1,000 or more on the high end. Whole-home filters are more complex and usually start out at around $400 and could go up to more than $10,000 on the high end. [5]

Sources:

  1. “History of Reverse Osmosis.” Reverse Osmosis Water Filters Buyer’s Guide, www.reverse-osmosis-water-filter-guide.com/history-of-reverse-osmosis.html.
  2. “7 Examples Of Osmosis In Everyday Life.” Udemy Blog, blog.udemy.com/examples-of-osmosis/.
  3. A. Sagle and B. Freeman “Fundamentals of Membranes for Water Treatment.” The University of Texas at Austin https://www.twdb.texas.gov/publications/reports/numbered_reports/doc/R363/C6.pdf.
  4. “Technical Information on Home Water Treatment Technologies CDC.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, www.cdc.gov/healthywater/drinking/home-water-treatment/household_water_treatment.html#osmosis.
  5. “Learn How Much It Costs to Install a Water Treatment & Purification System.” 2019 Water Treatment System Costs. www.homeadvisor.com/cost/environmental-safety/install-a-water-treatment-and-purification-system/.