A reverse osmosis water filter is a convenient way to ensure that your family has constant access to clean, clear, healthy drinking water. This type of filter system uses no power and requires no input after fitting until it’s time to change the filters or perform the recommended annual cleaning. The best reverse osmosis water filter system could be the perfect solution for clean drinking water.
As well as being low maintenance, reverse osmosis systems are extremely effective and can remove most contaminants, including lead, from drinking water. In fact, this technology is used in the military, medical facilities,and food and drink industries to ensure health and safety. If you are concerned about possible health problems caused by contaminated water, or old water pipes, then a reverse osmosis system is likely to be the best fit for your home.
How Does a Reverse Osmosis Water Filter Work?
In this type of water filtration system, pressure is used to force water through a semipermeable membrane. This membrane passes water molecules through easily, but larger ones like chemicals, bacteria, and viruses are trapped on the other side.
Reverse osmosis can remove salt, magnesium, potassium, copper, barium, chromium, nitrates, arsenic, lead, and some man-made chemicals from your drinking water. Water that passes through the membrane is purified and cleaned ready for all your household needs, including drinking and cooking.
What about the water left behind…
The ‘contaminated’ side of the membrane still contains water, but this water is considered ‘waste’ as it now has a much higher concentration of minerals, chemicals, and bacteria. One of the disadvantages of reverse osmosis systems is that one gallon of purified water can result in as many as five gallons of ‘contaminated’ water.
This water is sometimes flushed away, despite the fact that it is still drinkable according to government standards. Environmentalists argue that this wastes water and results in a higher concentration of contaminants in our rivers and streams. Some systems try to solve this problem. One way to avoid wasting the water is to direct it to the hot water system for use in hand washing, while another way is to return it to the filtration system for re-filtering.
If the unit re-filters contaminated water it can cause extra wear and will result in filters needing to be replaced more often.
What Types of Reverse Osmosis System are Available?
Most household reverse osmosis systems are relatively similar. Point of Entry systems filter water as it enters your house, so that every room in the home – the bathroom, sinks, washing machine – use filtered water. Point of Use systems are more common and are typically more affordable. They consist of a dedicated faucet, filters and a tank which usually sits under the sink, and have a number of different filtration stages.
The main differences between systems will be the number of stages included, and the quality of the parts. Filters also differ in the amount of water they process – this is measured in gpd, or gallons per day.
A typical 5 stage system will have the following parts:
Pre-Filter(s) – water from your home’s cold water supply arrives here first. The Stage 1 pre-filter is usually a sediment filter. The Stage 1 filter’s job is to protect the reverse osmosis membrane from clogging by removing larger particles of sand, dirt and silt.
Next, a Stage 2 carbon filter removes cloudiness, odors, and unpleasant tastes. At this stage, if you have chlorinated water, a Stage 3 carbon filter is needed to remove chlorine to avoid membrane damage.
Reverse Osmosis Membrane – (Stage 4) removes substances like fluoride, arsenic, lead, pathogens, and any dissolved solids larger than the water molecules. This is the main part of the system, and there are different types of filters available (see below) for different applications. After treatment here, water will be clearer, safer, and better tasting than tap water.
Post-Filter – This Stage 5 carbon filter is the water’s final stop on its journey to your faucet. This filter will remove remaining traces of taste or odor.
Storage Tank – This usually measures around 15 inches by 12 inches, and holds between two and four gallons of filtered water. This water is pressurised by a bladder inside the tank which helps turn off the filtration process when the tank is full.
Valves and Flow-Restrictor – Valves stop the reverse osmosis system drawing water from the supply when the tank is full. They also prevent any water flowing back through the system to prevent damage to the membrane.
The flow restrictor is usually included as a part of the drainage system which helps keep the pressure up on the contaminant side of the membrane. This continually forces water through the membrane, allowing the system to process its maximum gallons per day.
Faucet – Reverse osmosis systems typically have their own faucet which needs to be installed on the kitchen sink.
Drain Line – This pipe takes contaminated water away from the system to the drain. Some systems conserve this water for use in the hot water system for hand washing, while others return the water to be filtered again.
There are different types of membranes available for household reverse osmosis systems. The most common are CTAs (cellulose triacetate membranes) and TFCs (thin film composite membranes). A TFC can remove a higher percentage (98 %) of contaminants, but will only work if your water is chlorine free. If you live in an area with chlorinated water, then you will need a carbon pre-treatment filter in addition to your reverse osmosis system.
CTAs can operate with chlorinated water, but they only remove around 93 percent of contaminants. Some manufacturers offer other types of membranes for use in industry, the military, and at sea for example.
Additional Filtration Stages
Having extra filters working in conjunction with a reverse osmosis system is common. As we mentioned above, a pre-treatment filter can remove chlorine from water. Another addition that can provide a valuable extra stage of purification is an ultra-violet light filter. These can remove microorganisms that manage to pass through any tiny defects in a membrane, giving added reliability.
How to Maintain a Reverse Osmosis System.
Your reverse osmosis system will last for many years if it is cleaned and maintained regularly. Once a year the system will need to be thoroughly cleaned, either by yourself or a technician.
You will need to change out filters according to the manufacturer’s instructions, but the following gives a general guide.
- Pre-Filter – change every 6-12 months
- Reverse Osmosis Membrane – change every 24-36 months
- Post-Filter – change every 12 months
Advantages of Reverse Osmosis Water Filter System
- Highly effective at removing contaminants, including viruses, bacteria, lead, and chemicals
- Improved water taste and odor
- Low maintenance
- Uses no electricity
- Costs less than using bottled water
- More environmentally friendly than using bottled water
Disadvantages of Reverse Osmosis
- Relatively slow compared to other filtration systems
- Can be inefficient – the most efficient systems will discard one gallon of wastewater for each gallon of drinking water produced. Less efficient systems can produce as much as five gallons of wastewater per gallon of drinking water
- Removes some healthy minerals such as magnesium, calcium, iron and sodium
- Can make water slightly acidic, due to removal of minerals
What About Minerals – Don’t We Need Those?
Yes – we do need minerals in our diet, and drinking water contains healthy amounts of sodium, calcium, magnesium and iron. The removal of these minerals by the reverse osmosis membrane changes the pH value of the drinking water, making it slightly acidic.
An additional pH filter in the reverse osmosis system will add minerals back into the water. This pushes the pH value back to a healthy, neutral pH7.
How Much Drinking Water Will a Reverse Osmosis Filter Produce?
Most manufacturers measure the amount of water processed by a filter system in gallons per day (gpd). An undersink system will be able to process a maximum between 50-90 gpd. The actual amount processed will depend on a few factors. First, the pressure of your water supply. Second, the temperature of the water as it enters the system. And third… how much filtration the water actually needs.
Most experts recommend that we each drink about a half a gallon of water per day. So, even the smaller systems will produce plenty of water for the biggest of families.
Is a Reverse Osmosis System Cost-Effective?
If a family of four were to buy bottled water to drink they could easily spend nearly $4000 every year. The average reverse osmosis system costs only $100 a year to run. Clearly, the cost of producing clean healthy water at home is much lower than buying bottled water.