What is reverse osmosis?

Clean, reliable drinking water matters in every home. Whether you are preparing meals, making coffee, or filling your child’s bottle, what comes from your tap affects daily wellbeing. If you want fewer contaminants and better taste from your tap, reverse osmosis (RO) is a simple, proven solution. This guide explains how it works and how our countertop and under-sink reverse osmosis units fit into everyday life.

What is reverse osmosis?

Osmosis is water moving through a membrane from a weaker solution to a stronger one. Reverse osmosis does the opposite. It uses pressure to push water through a very fine, semi-permeable membrane. Most dissolved substances are left behind.

A reverse osmosis system is designed to separate two streams. The permeate is the cleaned water you drink. The concentrate is a small stream that carries away the contaminants.

In a home setting, the membrane sits with carbon and sediment prefilters and a final carbon polish. Our countertop reverse osmosis units use an internal pump. You fill the tap-water tank and the unit produces purified water, which is dispensed into a clean Carafe or filtered tank.  Our Under Sink system connects to your water supply and refills its tank automatically for on-tap dispensing. Both formats use the same core technology found in the best reverse osmosis water filter designs.

Reverse osmosis has become the standard for household water purification due to its ability to remove up to 99% of harmful substances. We build on this technology with a patented 4-stage filtration system designed for maximum efficiency and ease of use.

What is reverse osmosis water?

Reverse osmosis water is water that has been filtered to remove nearly all contaminants and dissolved solids. It is significantly purer than standard tap water, which may contain traces of chlorine, lead, industrial residues, and other impurities.

All of our models purify water in four distinct stages—mechanical filtration, carbon pre-treatment, reverse osmosis, and a final activated carbon stage. The result is clean, fresh-tasting water suitable for drinking, cooking, and even for pets and plants.

What is the purpose of reverse osmosis?

The primary goal of reverse osmosis is to make water safer and more enjoyable to drink. It removes contaminants that may affect your health over time and eliminates unpleasant taste and odour.

It also offers long-term environmental benefits by reducing dependence on bottled water, which in turn cuts down plastic waste. From a financial perspective, a home filtration system is far more cost-effective over time than buying bottled water regularly.

Explore more: The importance of drinking water

How does reverse osmosis work?

Think of reverse osmosis as a highly advanced sieve that allows only clean water to pass through. The process involves four stages:

1. Mechanical filtration – traps larger particles such as rust and limescale.
2. Pre-carbon filtration – reduces chlorine and chloramine, which can damage the membrane and affect taste.
3. Reverse osmosis membrane – filters out dissolved solids, heavy metals, and chemical residues.
4. Activated coconut carbon filtration – enhances taste and provides the final polish.

AquaTru’s patented 4-stage system combines these processes into a single, compact design that delivers exceptional results with minimal maintenance.

Countertop models use a built-in pump. You pour tap water into the tank and the unit does the rest. No plumbing is needed.

Under-sink models use your mains water pressure. They refill themselves and are always ready at the tap.

What are the components of a reverse osmosis system?

A standard RO system includes:

• A prefilter to capture particles and sediment.
• A carbon filter to reduce chlorine and improve taste.
• A reverse osmosis membrane that removes most dissolved contaminants.
• A post-filter to ensure the water is fresh and clean when dispensed.
• Optional: A tank or outlet for convenient access to filtered water.

AquaTru integrates these elements in one certified, easy-to-use appliance.

Which minerals can RO remove from tap water?

Reverse osmosis is highly effective at removing many of the most concerning contaminants found in tap water. These include:

• Lead
• PFAS
• Chlorine
• Fluoride
• Glyphosate
• Arsenic
• Nitrates
• Mercury and other heavy metals
• Microplastics

These substances are often present in trace amounts but can build up with long-term exposure. While not always visible or noticeable in taste, each of these contaminants can pose serious health concerns over time.

While most reverse osmosis systems reduce many of these, AquaTru has been independently tested to remove up to 99%, including a wide range of additional substances not always addressed by standard filters.

Check our performance data sheets to see exactly what AquaTru removes.

What are the advantages of reverse osmosis filtration?

Reverse osmosis systems offer meaningful everyday benefits for households, both in health and convenience. Let’s discover some benefits of filtered water:

• Cleaner, safer water – reduces exposure to up to 99% of contaminants, including chemicals, heavy metals, and microplastics.
• Better taste and clarity – removes chlorine, odours, and aftertastes that affect how water tastes and smells.
• Less reliance on plastic – supports a more sustainable lifestyle by reducing the need for bottled water.
• More efficient use of water – AquaTru uses far less water than standard systems, discarding just one litre for every three litres filtered. The remaining water can be reused for non-drinking purposes like watering plants.
• Cost savings over time – eliminates ongoing purchases of bottled water, making it a smart long-term investment.
• Everyday wellbeing – enhances hydration, supports cooking, and fits easily into wellness and skincare routines.

What is the disadvantage of reverse osmosis filtration?

Reverse osmosis systems discard some water during filtration. While standard systems waste more than two litres for every three litres filtered, AquaTru is designed to be highly efficient, with a 3:1 clean-to-waste ratio.

Another consideration is mineral loss. Reverse osmosis removes some naturally occurring minerals. However, these are present in small amounts, and essential minerals are best obtained from food. We offer remineralisation options, such as Perfect Minerals or the pH+ VOC (Alkaline) filter.

Reverse osmosis vs. other water filtration methods

Compare what each method removes and where it fits. See our guide to how different water filters work below:

Is drinking water from an RO system too pure and therefore dangerous?

No. Reverse osmosis water is not “too pure” or dangerous. It’s just clean—safe, healthy, and ideal for drinking.

What is “ultrapure” water?

Ultrapure water is used in industries like electronics and lab work. It has nearly all dissolved substances removed—down to about 0.03 mg/L of total dissolved solids (TDS). This kind of water is not made for drinking. It can even damage pipes or equipment because it wants to dissolve everything it touches.

How pure is RO water at home?

Home RO systems are very different. They don’t make ultrapure water.

• A typical RO membrane removes about 95% of TDS.
• If your tap water starts at 400 mg/L TDS, the RO water will be around 20 mg/L.
• Over time, a bit of salt may pass through when the system is off—this is called TDS creep. So, stored water may rise slightly, often to about 10% of the original TDS.

This is still well within safe limits for drinking water.

Why is RO water a great choice?

• It’s clean but not extreme — enough contaminants are removed to protect your health, but not so much that it becomes chemically unstable.
• It meets safety standards — naval vessels use multi-pass RO systems that produce even lower TDS water (<1 mg/L) for drinking.
• It’s similar to natural low-TDS water — cities like Vancouver, Canada, have natural water with only 12–25 mg/L TDS. People drink it daily without problems.
• Water’s job is hydration — not nutrition. You get minerals from food, not from trace amounts in tap water.

RO water is not “too pure”—it’s just right. Not dangerous. Not industrial. Just fresh, filtered water that’s safe and healthy to drink every day.

Other myths and facts about reverse osmosis

“We need minerals from drinking water for good health.”
Fact: Food provides almost all the minerals your body uses. The small amount in tap water is not essential for nutrition. A reverse osmosis filter removes dissolved substances, including harmless minerals, without creating a nutrition gap.

“RO systems waste too much water.”
Fact: The modern designs of AquaTru are much more efficient and send a concentrate stream to drain only while making purified water. Many households reuse that non-drinking water for suitable tasks such as watering plants. AquaTru is one of the most water-efficient water filter systems on the market.

“RO water does not taste good.”
Fact: Off-tastes usually come from chlorine. RO systems include carbon filters that remove chlorine, so the taste is clean and neutral. Chill it or add fruit and herbs if you prefer more flavour using the AquaTru Carafe - Infuser Lid with Glass Pitcher. 

“RO removes bacteria completely.”
Fact: RO filters water but does not sterilise it. It is designed for microbiologically safe mains water. Small numbers of harmless bacteria can exist in storage tanks without causing illness or taste. Follow the filter-change schedule and simple cleaning steps.

“RO strips out everything, so it must be unhealthy.”
Fact: RO targets dissolved contaminants you do not want to drink, such as lead, arsenic, nitrates, fluoride and PFAS. Your diet supplies essential minerals. Remineralise for taste if you like, but it is not required for health.

“Countertop RO and under-sink RO work differently.”
Fact: Both use the same membrane process. Countertop models use an internal pump and a removable carafe. Under-sink models use mains pressure and refill automatically. Choose the format that fits your space and routine. Water quality is the same.

“RO is complicated to use and maintain.”
Fact: Day-to-day use is simple. Countertop units are plug-and-play. Under-sink units dispense from your existing tap. Replace prefilters on schedule and follow quick cleaning steps. Many users find this easier and more economical than buying and storing bottled water.

Where is reverse osmosis used today?

Reverse osmosis is trusted worldwide for its ability to produce consistently clean, safe water. It plays a vital role in a range of sectors where water quality cannot be compromised:

• Households – used daily for drinking, cooking, and improving overall water quality at home.
• Hospitals and healthcare – essential in dialysis treatment and sterile environments where high-purity water is required.
• Food and beverage production – ensures consistency, safety, and flavour in products ranging from bottled drinks to processed foods.
• Emergency and disaster relief – deployed in situations where clean water is scarce or contaminated.

From domestic use to critical healthcare and large-scale manufacturing, reverse osmosis is a proven solution relied upon globally to support health, safety, and quality.

How can you produce fresh water through reverse osmosis?

A home RO system makes it easy to produce fresh water on demand. Our countertop models are plug-and-play and require no plumbing, while the under-sink model connects directly to your water line and dispenses purified water from your existing tap. By selecting the best reverse osmosis filter for your space and routine, you’ll enjoy reliable, great-tasting water every day.

AquaTru: the best reverse osmosis drinking water filter in the UK

Every AquaTru model is built with the same patented 4-stage filtration technology, delivering the same high-performance water purification across the range. Whether you choose the Classic, the Carafe, or the Under Sink system, you can expect the same exceptional contaminant reduction and clean, great-tasting water.

• Countertop systems (Classic and Carafe) are plug-and-play units that require no plumbing or installation. They’re compact, portable, and easy to move—ideal for renters, frequent movers, or anyone wanting pure water without drilling or permanent fixtures.
• The Under Sink system integrates directly with your tap for a built-in solution. It offers a larger 7-litre capacity, automatic refill from your mains supply, and a clutter-free countertop.

Whether you prefer a portable countertop model or the fully integrated Under Sink system, AquaTru delivers the same high standard of water purification.

Order your AquaTru water filter system today!

Related reading:

• How can I purify my water at home?
• Understanding AquaTru filters: types, benefits and compatibility
• Reverse osmosis for pure, refreshing water