What is water recycling and how does it work?

Ever wondered where water goes once it flows down the drain or gets flushed down the toilet? What if we told you it could eventually come out your tap again (after a good clean, that is)?

Water recycling describes the process of purifying treated wastewater so it can become a supply source once again.

Its uses vary from drinking water, which requires the most rigorous processing, to industry or farming, where the water may need less filtration to be reused.

Water recycling means we use less fresh water. Essential for all living beings, fresh water only makes up 3% of our planet’s water, and less than half of that is available in liquid form.

As such, finding alternative water sources is going to be critical as demand grows and we face the challenges of climate change, such as more droughts.

How does water recycling work?

The usual water cycle sees us take water from rivers, aquifers and reservoirs, which is then processed (removing any harmful substances) for human use.

After it’s fulfilled its purpose and becomes waste (like grey water), it’s sent to a wastewater treatment facility and then released back to the environment (to rivers or the sea) for the process to start again.

Recycling takes the wastewater that would normally go back to the environment so it can undergo more advanced processing.

As such, this source doesn't rely on rainfall and is therefore resilient to droughts.

Direct vs indirect water recycling

Water recycling can be direct or indirect.

Direct means the processed wastewater goes into existing water treatment works to then be distributed. Usually, this would be non-potable water (not suitable for drinking) used for things like industrial processes (for example, to cool down equipment).

Indirect recycling means it’s discharged into an environmental buffer, such as a river or a reservoir, where it mixes with other sources. It’s then taken to a drinking water treatment plant before being supplied for human use.

Ways to purify wastewater

Whether it’s direct or indirect recycling, water will need to go through advanced treatment processes at a water recycling plant. Which processes are used depends on its ultimate purpose.

Treatment methods include:

• Activated sludge: uses microorganisms to consume organic pollutants such as pesticides
• Membrane filtration: pushes water through very fine membranes at high pressure, which can filter out tiny particles
• Reverse osmosis: the most precise form of membrane filtration, it separates water molecules from other substances (it can even remove dissolved salts)
• Disinfection: aims to kill pathogens using ultraviolet light and chemicals such as chlorine and ozone

Is recycled water safe to drink?

To be consumed by humans, recycled water must meet strict quality standards that cover things like:

• Microorganisms
• Chemicals such as pesticides
• Metals such as lead or copper
• Look and taste

The independent drinking water regulator for England and Wales is called the Drinking Water Inspectorate.

It works to ensure water companies meet the quality obligations set out in the Water Industry Act 1991. 

Where is wastewater recycling already being used?

Recycled water is used in countries like Australia, Namibia, South Africa and the US.

But Singapore stands out for applying it at a large scale. Its recycled wastewater, known as NEWater, can meet up to 40% of the city-state's entire demand for drinking water.

The idea to recycle water first came up in the early 1970s. It was then revisited and trialled in 1998.

The trial's success in terms of quality and drinking water standards led Singapore to plan a full-scale rollout.

Importantly, Singapore’s government led an outreach campaign to get the public onboard with using NEWater and overcome the so-called ‘yuck factor’.

For more information about water recycling and how it could be used in the UK, read the 2025 State of the Nation report.

Read the report

Water recycling’s role in creating a sustainable and resilient supply

Singapore’s NEWater featured in Professor Jim Hall’s presidential address in 2024.

Prof Hall talked to William Yeo from Singapore’s National Water Agency about the city-state's four national taps. Watch the clip: