The Scottish Government

Total Coliforms

PCV 0 per 100ml

Sampled at WTW, service reservoirs and at consumers' taps.

The coliform group of bacteria is present in large numbers in the gut of all warm-blooded animals and in the environment. Their presence in water supplies may indicate a breach in the integrity of the water supply system or a failure of the treatment process, and they are a useful indicator in monitoring the quality of water supplies. It is generally considered that coliforms themselves do not present a risk to health, and on their own they do not indicate that faecal pollution has occurred.

Faecal Coliforms

PCV 0 per 100ml

Sampled at WTW, service reservoirs and at consumers' taps.

Faecal coliforms are present in large numbers in the gut of all warm-blooded animals. Their presence in water supplies indicates a breach in the integrity of the water supply system and that faecal pollution may have occurred. The detection of faecal coliforms in a water supply is taken very seriously.

Colour

PCV 20 mg/L Pt/Co

Sampled at consumers' taps.

True colour in water comes from naturally occurring humic substances, particularly in acidic water sources derived from peaty moorland catchment areas with minimal treatment. High colour may be unacceptable to consumers on aesthetic grounds and the humic substances may form other compounds such as trihalomethanes when the water is disinfected.

Turbidity

PCV 4 NTU

Sampled at consumers' taps (1 NTU standard applies at treatment works).

Turbidity is a measure of the "cloudiness" of the water. Naturally occurring turbidity is usually caused by the suspension of tiny particles of predominantly inorganic origin. Its presence could indicate poor control of the treatment process and could mean that the treatment process has not provided an effective barrier against organisms such as Cryptosporidium, or that disinfection has been compromised.

Hydrogen Ion (pH)

PCV 6.5 - 9.5

Sampled at consumers' taps.

pH is a measure of the hydrogen ion content of the water or degree of acidity. Most surface waters in Scotland have a low pH and would therefore be corrosive towards the materials used in water treatment systems and consumers' installations unless corrected during treatment. Extreme pH values may present a risk to the health of consumers.

Aluminium

PCV 200 µg/l

Sampled at consumers' taps.

Aluminium occurs in acidic waters derived from moorland catchments and is removed in water treatment by coagulation and filtration. Aluminium sulphate is used as a coagulant in water treatment. High concentrations are unacceptable to consumers on aesthetic grounds.

Iron

PCV 200 µg/l

Sampled at consumers' taps.

Iron is present naturally in many water sources and is removed by conventional water treatment processes. Iron in water supplies may also be derived from corrosion of iron water mains and poor control of water treatment processes. High iron concentrations are unacceptable to consumers on aesthetic grounds as they may cause discoloured supplies.

Manganese

PCV 50 µg/l

Sampled at consumers' taps.

Manganese occurs naturally in many water sources. It may be removed from water by using an appropriate treatment process. Where treatment processes do not remove manganese, it may accumulate in water mains and cause unacceptable discolouration of supplies.

Lead

PCV 25 µg/l

Sampled at consumers' taps (reduces to 10µg/l in 2013).

Elevated lead concentrations may be present at consumers' taps if lead pipes have been used in the internal household plumbing or service pipe. Many waters in Scotland have a tendency to dissolve lead from lead pipework, and phosphate compounds can often be dosed at the treatment works to reduce this tendency.

Trihalomethanes

PCV 100 µg/L for total of four of the compounds.

Sampled at consumers' taps.

Trihalomethanes ( THMs), occur in drinking water principally as products of the reaction of chlorine with naturally occurring organic materials such as humic acids. Treatment processes can be adapted to minimise their formation or to remove the precursor compounds. THMs at high concentrations may present a health risk if consumed over a long period.