What is Reverse Osmosis?
Reverse osmosis removes contaminants from unfiltered water, or feed water, when pressure forces it through a semipermeable 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 pre-filter before it forces water through a semipermeable membrane to remove dissolved solids. After water exits the RO membrane, it passes through a post-filter to polish the drinking water before it enters a dedicated faucet. Reverse osmosis systems have various stages depending on their number of pre-filters and post-filters.
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:
- Sediment filter: Reduces particles like dirt, dust, and rust
- Carbon filter: Reduces volatile organic compounds (VOCs), chlorine, and other contaminants that give water a bad taste or odour
- Semi-permeable membrane: Removes up to 98% of total dissolved solids (TDS)
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.
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 odours, and the sediment filter removes dirt and debris.
Does a reverse osmosis system remove…
- Fluoride? Yes.
- Salt? Yes.
- Sediment? Yes.
- Chlorine? Yes.
- Arsenic? Yes.
- VOCs? Yes.
- Herbicides and pesticides? Yes.
- Many other contaminants? Yes. The contaminants listed are some of the most popular ones treated with an RO system, but the system also 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.
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