Our drinking water standards and water quality checks

 pH (Hydrogen ion concentration) describes the degree of acidity or alkalinity. Different minerals and other substances can affect this. The regulatory range for the pH of tap water in the UK is 6.5 to 9.5. 

The colour of drinking water is usually down to naturally occurring matter, but the presence of iron sediment caused by old cast iron pies may also have an impact. The PCV for colour is 20 degrees Hazen (°H). 

We measure water clarity (the amount of light that can travel through water) to determine the presence of things like clay, silt, algae, or other organic materials. Specialist devices call turbidimeters, shine a light through the sample to measure the intensity of light, or cloudiness of the water. Turbidity is closely monitored during the treatment process.  

Sometimes, water coming out of the tap has a milky/white appearance. This is usually caused by excess air dissolving in the water and isn't harmful. The PCV for turbidity at customers’ taps is 4.0 NTU. 

Occasionally customers contact us about the taste and smell of their water. The laboratory has a specialist panel of analysts who conduct blind tests on water samples to evaluate the quality. The panel are specifically trained to smell and taste water samples against a set of descriptors which can help identify any issues. 

Conductivity is a measure of the ions dissolved in water. It's often used to indicate the presence of trace levels of dissolved mineral salts of calcium, magnesium and sodium.  The PCV for conductivity is 2500 uS/cm at 20oC. 

We add chlorine in strictly controlled amounts during treatment to disinfect water and make sure it’s free from harmful bacteria and viruses. A small amount of ‘residual’ chlorine remains in your water after treatment to maintain its quality as it makes its way through the distribution network (the pipes).  

Chlorine levels are monitored at our water supply works, service reservoirs and at taps using field monitoring kits. It’s harmless to people in small concentrations which is why we only add it in strictly controlled amounts. No PCV is set for chlorine.  

If present, these may indicate an issue within the supply network as the treatment process removes and kills these organisms. As bacteria can flourish in taps, be careful not to contaminate your drinking water by keeping your taps clean. Be especially careful when washing food, as bacteria can easily splash back onto the tap. The PCV standards are 0 per 100 ml for E.coli and 0 per 100 ml for Enterococci. 

Traces of nitrate and nitrite can sometimes be found in drinking water. Farming can cause an increase of nitrate in raw untreated water. It’s used mainly in inorganic fertilisers. It also occurs naturally in plants and is a key nutrient that helps them grow. Where necessary, during the treatment process we remove nitrates or use blending to reduce the levels.   

Nitrite can form in drinking water pipes when bacteria grow in water that has been sitting still for a long time, especially if the water contains nitrate and has very little oxygen. 

• The PCV for nitrite is 0.5 mg NO2/l
• The PCV for nitrate is 50 mg NO3/l. 

Chloride in drinking water comes from natural sources such as mineral deposits, and from tidal mixing of river and groundwater. It can affect the taste of your water. The PCV for chloride is 250mgCl/l. 

We don't add fluoride to water, but it can be found naturally in raw water supplies at low levels. The PCV for fluoride is 1.5mgF/l. 

Copper occurs naturally and is normally found in low concentrations in drinking water. Issues with domestic plumbing and fittings can cause higher-than-normal levels of copper. The PCV for copper is 2mgCu/l. 

Iron is one of the most abundant metals on earth and is found naturally in surface and groundwater. After treatment, it’s normally reduced to trace concentrations in drinking water. Increased levels can happen because of corrosion in old cast iron water mains sediment. Normally there’s no health risk associated with higher levels of iron except in the case of some specific medical conditions. But iron can cause staining on domestic fittings and the water may look unacceptable to some.

The PCV for iron is 200ugFe/l.

Manganese occurs naturally, often because of the soil or sediment in natural water sources. High concentrations of manganese can affect how your water looks and can leave purple or black spots on your laundry. The PCV for manganese is 50ugMn/l. 

Aluminium can also occur because of soil or sediment in natural water sources. We use aluminium salts in the treatment process to help remove impurities. These are removed through the clarification and filtration processes.The PCV for aluminium is 200ugAl/l. 

Water leaving our supply works does not contain lead and we like to make sure it stays that way. Lead isn’t normally present in water sources, but significant concentrations can occur in drinking water if domestic lead pipes, or copper pipes with lead solder have been used in your plumbing. The PCV for lead is 10ugPb/l. 

Phosphate dosing is a treatment we use to prevent lead pipe work dissolving in water. We have it fitted at our water supply works where needed. When sampling specifically for lead, we take a first draw sample (first thing in the morning) and a flushed sample. 

Trihalomethanes (THMs) are by-product of the reaction chlorine has with naturally occurring, dissolved organic materials. In drinking water, we look at the sum of several compounds classed as THMs. The PCV for THMs is 100ug/l (sum of all compounds measured). 

In addition to the substances listed, we also carry out water quality tests for a wide range of compounds that include: 

• hydrocarbons
• pesticides
• herbicides
• phenols
• organic carbon. 

We also carry out extensive monitoring of our water supplies for cryptosporidium (a parasite that can cause diarrhoea) through sampling of raw and treated water.