What is Reverse Osmosis and How Can It Make Your Water Better?

Reverse Osmosis (RO) is a water filtration technology in which tap water is pushed through a semipermeable membrane (resembling an extremely fine cloth) by the mains water pressure. The membrane does not allow larger molecules or microorganisms to pass through so they are retained on one side of the membrane while the purified water emerges on the other side. 

What are the ‘’stages” of Reverse Osmosis?

Reverse Osmosis filtration systems are usually described with the number of stages in the filtration process. A RO system might mention 3 stage filtration, 5 stage etc. 

In fact, the actual Reverse Osmosis membrane is one (the main one!) step in the filtration process, and the system contains other filters in addition to the RO membrane. Typically you will have two or three pre-filters that prepare the water before it goes through the RO membrane, removing some impurities (and prolonging the life of the RO membrane) as well as one or two filters that after that. 

A typical 5-stage RO system might include:

-- Stage 1: polypropylene foam filter to remove sand, rust, silt etc.

-- Stage 2: activated coconut shell carbon and polypropylene material to remove chlorine and organic compounds.

-- Stage 3: activated carbon block to remove a higher proportion of chlorine and some organic compounds. 

-- Stage 4: Reverse Osmosis membrane.

-- Stage 5: inline filter containing deionisation resin to further reduce total dissolved solids (TDS) in the produced water

What contaminants are removed by Reverse Osmosis filtration systems?

RO filtration systems similar to the one described above remove pretty much every contaminant found in tap water, including (but not limited to):

-- Lead and other heavy metals,

-- Chlorine and chloramines,

-- Pesticides,

-- Microplastics and microfibres, 

-- Fluoride,

-- Detergents,

-- Nitrates & Sulfates,

-- Salt. 

The water produced by a Reverse Osmosis system is indeed very pure. In fact, the RO filtration process removes not just the harmful and undesirable compounds but also some beneficial minerals. That’s why RO systems used for drinking water contain a remineralisation module. For other uses, however, the purer, the better. That’s why RO is a filtration system particularly favoured by window cleaners and owners of aquaria!

Pure Water Window Cleaning

Water is an excellent solvent, which is why it has great cleaning properties. The purer the water is, the better it cleans -- so much that the highly purified water obtained through Reverse Osmosis can be used to effectively clean windows without any additional detergents. It attracts dirt, making cleaning easy and efficient, and, as it doesn’t contain impurities, it leaves no residue. This also keeps the windows clean for longer. 

Reverse Osmosis is particularly suitable for purifying water to supply  Water-fed Pole window cleaning systems used by professional window cleaners. 

Water for Aquaria

Fish live in water and “breathe” water, and the overall quality (including purity) of the fishtank water is absolutely crucial to their well-being and survival. 

Unfiltered tap water contains chlorine, chloramines, nitrates, phosphates, heavy metals and numerous other chemicals that can negatively affect sensitive aquatic organisms (particularly corals in marine aquaria), both directly and through unwanted growth of algae. Specific requirements of various species of fish vary, and depending on the species, the water might require addition of various compounds to remineralise it. The latter is crucial for freshwater fish.

In every case though, using water purified by RO will allow the owner to create optimal conditions for their aquarium. 

Practical matters and issues to consider

Reverse Osmosis systems are easy to install by a competent DIY-yer or handyman and don’t usually require services of a plumber.  

A typical RO filtration system consists of the filter unit fed from the mains water supply and a storage tank. It doesn’t need electricity to power it, so after the initial outlay, day-to-day running is free. As the reverse osmosis process relies on pressure of water supply, in the unlikely case your water pressure is lower than 40 psi (3 bar), an additional pump might be needed. 

The filters require replacement every 6 months to maintain the performance of the system. The membranes need replacing about every 3 years, depending on the characteristics of your tap water. 

Reverse Osmosis is a fairly slow process (systems differ by their output, with a typical under-sink system able to produce up to about 50 gallons per day), though the main limiting factor is the capacity of the storage tank as the filtration process stops when the tank is full. 

About 70-80% of the feed water is discarded (usually to wastewater) during Reverse Osmosis filtration, so this is an environmental (and, if you have metered water, financial) consideration when choosing a water filtration system for domestic purposes. 

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