What is reverse osmosis?
Reverse osmosis removes contaminants from unfiltered water, or feed
water, when pressure forces it through a semi permeable membrane.
Water flows from the more concentrated side (more contaminants) of the RO
membrane to the less concentrated side (fewer contaminants) to provide clean
drinking water. The fresh water produced is called the permeate. The
concentrated water left over is called the waste or brine.
A semipermeable membrane has small pores that block contaminants but allow
water molecules to flow through. In osmosis, water becomes more concentrated
as it passes through the membrane to obtain equilibrium on both sides. Reverse
osmosis, however, blocks contaminants from entering the less concentrated side
of the membrane. For example, when pressure is applied to a volume of
saltwater during reverse osmosis, the salt is left behind and only clean water
flows through.
How does a reverse osmosis
system work?
A reverse osmosis system removes sediment and chlorine from water with a
prefilter before it forces water through a semipermeable membrane to remove
dissolved solids. After water exits the RO membrane, it passes through a
postfilter to polish the drinking water before it enters a dedicated faucet. Reverse
osmosis systems have various stages depending on their number of prefilters
and postfilters.
Stages of RO systems
The RO membrane is the focal point of a reverse osmosis system, but an RO
system also includes other types of filtration. RO systems are made up of 3, 4, or
5 stages of filtration.
Every reverse osmosis water system contains a sediment filter and a carbon filter
in addition to the RO membrane. The filters are called either prefilters or
postfilters depending on whether water passes through them before or after
it passes through the membrane.
Each type of system contains one or more of the following filters:
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Sediment filter: Reduces particles like dirt, dust, and rust
Carbon filter: Reduces volatile organic compounds (VOCs), chlorine, and
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other contaminants that give water a bad taste or odor
Semi-permeable membrane: Removes up to 98% of total dissolved
solids (TDS)
1. When water first enters an RO system, it goes through
prefiltration. Prefiltration typically includes a carbon filter and a sediment
filter to remove sediment and chlorine that could clog or damage the RO
membrane.
2. Next, water goes through the reverse osmosis membrane where dissolved
particles, even too small to be seen with an electron microscope, are
removed.
3. After filtration, water flows to the storage tank, where it is held until
needed. A reverse osmosis system continues to filter water until the
storage tank is full and then shuts off.
4. Once you turn on your drinking water faucet, water comes out of the
storage tank through another postfilter to polish drinking water before it
gets to your faucet.
Why do you need an RO storage tank?
An RO storage tank holds reverse osmosis water so you have plenty to use
when you need it. A reverse osmosis system makes water slowly. It takes one
minute to produce two to three ounces of RO water. If you were to turn on your
faucet for a glass of water at the actual membrane production rate, then you
would have to wait at least 5 minutes for it to fill. With a storage tank, your glass
fills instantly.
Read more about how a water storage tank works.
What does a reverse osmosis
system remove?
A reverse osmosis system removes dissolved solids like arsenic and fluoride
through the RO membrane. An RO system also includes sediment and carbon
filtration for a broad spectrum of reduction. The carbon filters in an RO system
remove chlorine and bad taste and odors, and the sediment filter removes dirt
and debris
Does a reverse osmosis system remove…
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Fluoride? Yes.
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Salt? Yes.
Sediment? Yes.
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Chlorine? Yes.
Arsenic? Yes.
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VOCs? Yes.
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Herbicides and pesticides? Yes.
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Many other contaminants? Yes. The contaminants listed are some of the
most popular ones treated with an RO system, but the system also
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removes a slew of other contaminants.
Bacteria and Viruses? No. If your water comes from a city treatment plant,
then it should already be microbiologically safe. Reverse osmosis may
remove some bacteria, but bacteria could grow on the membrane and
potentially enter your water supply. To remove living organisms and
viruses, we recommend UV disinfection.
Learn how to remove bacteria from your drinking water.
Reverse osmosis system benefits
A reverse osmosis system is one of the most extensive methods of filtration. It
removes 98% of dissolved solids, which makes it healthier to drink. A water
distiller is the only other drinking water system that also reduces TDS, but it's
less efficient than an RO system.
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Harmful dissolved contaminants reduced
Sodium reduced
Bad tastes and odors reduced
More environmentally friendly than bottled water
Easy to install and maintain
Fits under the kitchen sink
Browse Reverse Osmosis Systems
Does reverse osmosis waste water?
A reverse osmosis system sends water with rejected contaminants down the
drain as wastewater, unlike other filters that trap contaminants. As water flows
through the system, it's divided into two streams. One stream carries the filtered
water to a dedicated faucet, and the other stream carries the removed salts,
dissolved pollutants, and minerals to the drain.
The brine or "wastewater" carries rejected contaminants from a reverse osmosis
system to the drain. 4 gallons of water exits the drain for every gallon of water
produced. But the brine water is used for a purpose, so it's not exactly
wasted. The wastewater in an RO system helps clean the water, just like a
dishwasher uses water to clean dishes or a washing machine uses water to
clean clothes. However, it's our job in caring for the environment to minimize the
amount of water sent to the drain and increase the efficiency of the RO system.
How to reduce wastewater in an RO system
1. Add a permeate pump. Installing a permeate pump to a reverse osmosis
system is the best way to increase its efficiency. Permeate pumps reduce
the wastewater from an RO system by 75 to 80%. Not every reverse
osmosis system is designed to use one, so make sure the one you choose
is plumbed for an additional pump.
2. Choose an RO system with an automatic shut off valve. An ASO valve
stops the flow of water to the drain once the storage tank is full.
3. Use the RO reject water for landscaping or artificial lakes. Drain water has
higher levels of total dissolved solids (TDS), but it's safe to use in your
lawn or garden.
The Neo-Pure 4300 DLX is one of the most efficient RO systems because it
includes a permeate pump and an ASO valve.
Is reverse osmosis good for the environment?
When the water you use drains from your home, chemicals and other
contaminants must be removed before it's recycled. Wastewater is either sent to
a water treatment plant and diluted to make it easier to treat or to riverbeds for
nature to filter through the hydrologic cycle.
A reverse osmosis system makes waste treatment more efficient. Reverse
osmosis water drained from your home is already free of chemicals since they've
been removed in the carbon filtration stage. The leftover brine water has just a
slightly higher concentration of dissolved inorganics. RO systems speed up the
recycling process because no new chemicals are introduced into the water
supply after RO water drains from your house.