Water test kit: how and why we test for nutrient pollution

27th October 2025

Our testing kit enables everyone to test the water quality of their local rivers, streams, lakes and ponds. You can help to measure your local water quality as part of the biannual Great UK WaterBlitz, as an individual FreshWater Watcher, or as part of a community group.

In September 2025, over 6,000 people took part in the Great UK WaterBlitz. The results from their testing showed that 60% of freshwater sites in the UK had poor ecological health.

But what do we test for and how do we do it? Our previous Director of Science & Policy, Dr Sasha Woods, explains.

What do we test for and why?

Nitrates and phosphates are nutrients. Our testing kit measures the concentration (the amount of a component in a given area or volume) of nitrates and phosphates in fresh water.

Healthy freshwater bodies, such as rivers, streams, lakes and ponds, usually have low levels of these nutrients. They help aquatic plants to survive. However, high levels of nitrates and phosphates are bad news for waterbodies.

High levels of nutrients trigger a process called eutrophication. This is when excessive plant and algal growth leads to high levels of bacteria. The bacteria reduce oxygen levels in the water, killing plants and animals.

For that reason nitrates and phosphates are useful indicators of the ecological health of freshwater. This is the water’s ability to support healthy, diverse communities of plants and wildlife.

If a river has nutrient pollution and poor ecological health, it is unable to provide a healthy home for plants and animals.

Read our water pollution blog to learn more about the causes and effects of nutrient pollution on our waterways and wildlife.

How does our water testing kit work?

To measure nitrates and phosphates, 1.5ml samples of fresh water are added to the small nutrient tubes included in the testing kit. These tubes contain a reagent inside them. After a few minutes, the samples will change colour depending on how much nitrogen or phosphorus is present.

The higher the concentration of these nutrients in the water, measured in parts per million (ppm), the darker the colour. So the darker the colour, the higher the level of nutrient pollution.

We group measurements into acceptable water quality (<1.0 ppm N, <0.1 ppm P), i.e., showing evidence of low nutrient pollution, suggesting good ecological health. Or unacceptable water quality (> 1.0 ppm N, >0.1 ppm P), i.e., showing moderate to high levels of nutrient pollution, suggesting poor ecological health.

When citizen scientists measure the water quality, we also ask them to record some visual observations alongside. This includes how the surrounding land is used, and any pollution sources or algae they see.

They share their results on our FreshWater Watch platform contributing to our global data map. This data is open and accessible to everyone, helping us all to fight for clean and healthy fresh water.

What about measuring other types of pollution?

As well as nutrient pollution, our waterways are affected by a wide range of chemicals and bacteria, such as Escherichia coli (E.coli) bacteria.

Bacteria are single-celled organisms found everywhere including in rivers, streams, lakes and ponds. Most of these bacteria are harmless. However, certain bacteria have the potential to cause sickness and disease in humans and wildlife.

Coliforms are bacteria that live in the intestines of warm-blooded animals (such as humans, farm animals, pets and wildlife). Faecal coliform bacteria, including E.coli, are a kind of coliform found in human or other animal waste.

E.coli are a large group of bacteria. Most of them are harmless and are part of a healthy gut.

Both coliforms and disease-causing bacteria live in water. But unlike coliforms, disease-causing bacteria usually don’t survive long outside the body of animals. This means testing for disease-causing bacteria is difficult.

Scientists and public health officials test for E.coli and total coliforms as an indicator of disease-causing bacteria. But because E.coli is inside all warm-blooded animals it is difficult to learn where it comes from. High levels of E.coli could come from any animals, ranging from pets and livestock to human sewage and septic tanks.

So testing for other chemicals is useful to get a better idea of where the E.coli in that waterbody comes from, and what else might be polluting the water. However, testing accurately for other chemicals involves complicated methods and equipment.

How we are testing for other chemicals

As part of the Autumn Great UK WaterBlitz in September 2025, we partnered with Imperial College London and community groups to do some additional testing for other chemicals. Lab scientists analysed water samples using liquid chromatography–tandem mass spectrometry.

This method separates molecules in a liquid sample and calculates the weight of different components and their quantities. It can provide a “fingerprint” of a water sample; showing the presence and amounts of hundreds of chemicals.

Therefore, having that knowledge helps scientists understand the types of pollution and their sources in that sample. For example, identifying the difference between treated and untreated sewage.

We rely on funding to be able to supply additional kits and conduct specific research such as lab testing. Due to limited funding for the Spring Great UK WaterBlitz in April 2026, we will only be testing for nitrate, phosphate and pH.

How can you help?

Our freshwater habitats are in trouble and we need urgent action to make the invisible, visible. Take part in the next Great UK WaterBlitz between 24-27 April 2026 to join the fight for healthy freshwater! Help us build a national picture of water quality across the UK. Every datapoint counts.