ARSENIC (ug/l)
Naturally occurring, present in combination with sulphur and chelated (combined) to other metals. It is not a metal itself but has some metallic properties. A significant portion of arsenic found in fresh water is derived from industrial discharges, which are normally inorganic and tend to be more toxic that the organic variety.

Health implications
This is a health related parameter and therefore should be monitored carefully once detected at alert level.

The toxicity or arsenic depends on its chemical and physical form, the duration of the exposure and the age and sex of the exposed individual. The trivalent inorganic form is considered most toxic.

The WHO have set a guide level of 0.05mg/l.

CARBON DIOXIDE (calculated) mg/l
Carbon dioxide is often present dissolved in underground waters. In water it dissociates partially to form carbonic acid. This can be aggressive to mains, metal pipework and fittings under certain conditions of low alkalinity and pH. 

CHLORIDE (mg/l)
Chloride is widely distributed in nature usually in the form of salts of sodium, potassium and calcium. In fresh water it is derived from dissolution of salt deposits, salting of roads in winter and resultant run off, fertilizer run off, chemical effluents from industry, leachates from tips, sewage and irrigation drainage. 

Chlorides are useful to the operational scientist as an early warning of possible ingress into the supply and distribution system. 

Health implications
It is an essential element for the maintenance of healthy physiology, and is unlikely to be limiting in the temperate climate. Sensitive palates can detect a "salty" taste in coffee below the incident trigger of 400mg/l.

CHLORINE (free mg/l) and (total mg/l)
The use of chlorine for disinfection purposes is well documented in many texts on water treatment.

Health implications
Chlorine is a very powerful oxidising agent and in aqueous solution dissociates to give aqueous chlorine, chloride ion and hypochlorous ion. Concentrations of upto 50mg/l have not been reported to cause any adverse effects in man. Its reactions with ammonia and other contaminants give rise to organoleptic and toxic properties.

COLOUR (Hazen)
Colour is a physical characteristic of water. Some boreholes produce ferruginous waters but the majority of borehole sources will be clear and bright in appearance.

Health implications 
None.

CONDUCTIVITY (uS/cm)
Conductivity is a measure of a the electric current carried in the water by ionized substances. Water's with a high mineral content tend to have higher conductivities.

Conductivity is useful as an early warning of possible ingress into the supply and distribution system. 

Values often differ between source waters and can be a guide to blending proportions between them in distribution.

Health implications None directly, however the ionic charateristsics of the particles which make up the value may do on an individual basis.

CYANIDE (easily liberable ug/l) 
Cyanide occurs in two forms inorganic and organic (this group of chemicals are called nitriles). Cyanides are often metabolic intermediaries. They are used industrially to remove gold, silver, in steel production and electroplating. They are also used to fumigants, rodenticides, metal polishes and some photographic solutions.

Health implications
It is very toxic. It acts by blocking oxidative processes in the cells. Coma and fatalities can occur when the body's very efficient detoxification mechanism becomes overwhelmed.

DISSOLVED OXYGEN
This can be expressed as % Saturation at 20°C mg/l or mg/l at 20°C.

FLUORIDE (ug/l) 
Fluoride exists in a number of minerals e.g., fluorspar. It is quite common in the earth's crust and can give rise to natural enrichments of water passing over or through it. For this reason some underground sources in the company's catchment have a significant fluoride content. This will vary with water level in the boreholes which may be predicted.

Health implications
Consumption of water either naturally rich (<10mg/l) or artificially enriched (0.9-1.1 mg/l) are reported to have beneficial effects on teeth. Once incorporated into teeth, it reduces the solubility of the enamel under acidic conditions and hence helps to prevent dental caries (tooth decay).

In high doses fluoride is acutely toxic but this is unlikely to result from drinking water naturally or artificially rich in fluoride.

HARDNESS (as Ca mg/l)
Hardness is caused by polyvalent metallic ions dissolved in water, which in fresh water are principally magnesium and calcium. The Romany Lock supply is hard. Artificial softening is undertaken.

Health implications
None directly.

NITRATE (as N mg/l) or (as NO3 mg/l)
Nitrate in the environment is the end product of aerobic stabilization of organic nitrogen. It is one of the key limiting nutrients to plant growth on the earth. 

Health implications
Nitrate has health significance for infants whose gut physiology upto three months of age causes conversion of all ingested nitrate to nitrite. This prevents haemoglobin from carrying oxygen by oxidising it to methaemoglobin, which does not carry oxygen to the tissues. In severe cases Methaemoglobinaemia results, so called "blue baby syndrome" which can be fatal. (adults convert only ten% of ingested nitrate to nitrite). At double the incident level this potential condition is likely when water is used for making up baby feeds. 

Nitrosamines formed in the gut have been implicated in the formation of carcinogens. Evidence suggesting nitrate obtained from drinking water is a source of these compounds is inconclusive.

NITRITE (NO2 mg/l) 
Nitrite is formed by incomplete bacteriological oxidation of nitrogen. A group of bacteria called nitrosomonas perform this oxidation in soil or water where sufficient oxygen is present.

Health implications
As with nitrate.

The incident level is set three orders of magnitude below that of nitrate so methaemoglobinaemia is not likely to be a risk except under extremely rare circumstances.

AMMONIA (as NH4 mg/l) 
Ammonia is a colourless, pungent, gaseous, alkaline compound of hydrogen and nitrogen which is highly soluble in water. It is a biologically active compound present in most waters as a biological degradation product of nitrogenous organic matter. It can also get into ground and surface water through discharge of industrial wastes containing ammonia as a byproduct.

Ammonia is used as a part of the water treatment process. When added to the treatment process along with chlorine it can form chloramines which are a less powerful but more persistent disinfectant. These are of particular use when water has to travel large distances through intricate distribution systems.

Health implications
Ammonia is unlikely to cause direct effects because of its pungency, it would be too unpleasant to drink. Detection in treated water would suggest the disinfection process had failed or a major contamination of the distribution system had taken place.

KJELDHAL NITROGEN (as N mg/l) 
This is a measure of organic nitrogen in water. If investigating a nitrate incident it will allow the potential source or sources of pollution to be postulated. 

It is useful to distinguish nitrate from sewage pollution as opposed to inorganic nitrate fertilizer.

PERMANGANATE OXIDISABILITY (10 min mg/l)
This value is useful for the assessment of organic content of water at the works or in the distribution system. 

Health Implications
None. 

pH
pH is a measure of the hydrogen ion activity. It is strictly defined as the negative common logrithm of the hydrogen ion activity. It is interpreted to mean the "acidity" or "base" nature of a solution.

In most waters the acid-base realtionship is controlled by the chemical equilibria of the carbon dioxide - bicarbonate - carbonate ions. Factors such as temperature effect this system.

pH alteration occurs during treatment processes but should always remain within the range of 6.5 - 8.5 afterwards.

Health implications
No direct relationship. Changes in pH can effect the toxicity of some compounds e.g., ammonia.

PHOSPHOROUS (reactive ug/l)
Phosphorus combined as phosphate is one of the key limiting nutrients to plant growth on the earth. 

Health implications
In its elemental form as phosphorus it is very toxic, however it is usually found in water as phosphate, i.e., combined with oxygen as phosphate. 

SILICA (reactive as SiO2 mg/l)
Silica is the second most abundant element on earth. It is found in most raw underground and surface sources in the company's catchment.

Health implications
None.

SUSPENDED SOLIDS (at 105°C mg/l)
- see turbidity

This determinand should always be considered with turbidity. It gives a more precise measurement for non homogeneous mixtures of contaminants, e.g, algal breakthrough at a works.

SULPHATE (as SO4 mg/l)
Sulphates are used in detergents and hence can sometimes be used as an indicator of sewage ingress. Sulphates can also indicate pollution from tannerires, mining, steel mills and textile plants. Also can enter the water course from rainfall in urban areas as a result of burning fossil fuels.

Aluminium sulphate is used as a flocculant in chemical water treatment can will increase the natural content of the water.

High sulphates may contribute to the corrosion of metals in the distribution system, particularly waters having low alkalinity.

Health implications
Magnesium sulphate can act as a pugative on the gut.

SURFACTANTS (Cationic ug/l, Non Ionic ug/l, Anionic - Manoxol ug/l, Lauryl Sulphate ug/l

Surfactants are used as detergents or surface active agents. They are synthetic chemical compounds or cleansing substances used to emulsify dirt. They are usually made from aromatic sulphonates or alkyl sulphates 

Health implications
Likely to be unpalatable at concentrations high enough to give rise to problems. Detection in treated water is lilkely to be the result of pollution will have greater direct health significance.

TEMPERATURE (°C)
The rates of chemical reactions generally increase with increasing temperature. The concentrations of reactants and products in chemical equilibria can also change with temperature. At the normal range of temperatures encountered in works and distribution systems microorganisms which proliferate will generally be favoured by higher temperatures. Formation of some undesirable chlorination by products is favoured by higher temperatures e.g., Trihalomethanes.

Temperature can therefore affect every aspect of water supply and distribution and is of fundamental importance.

Health implications 
None directly.

TURBIDITY ( NTU)
This is a quick and easy measure of the suspended matter in water such as clay, silt, colloidal particles and microbiota. It is more practical that suspended solids for most purposes. It is used as an online monitor on water quality. Currently the nephelometric method is used for the measurement of turbidity. Nephlometeric turbidimeters measure the intensity of light scattered at 90 degrees to the path of the incident light. This measurement is expressed in NTU (nephelometric turbidity units).

The microbiological quality of the water can be affected by turbidity. Suspended particles may shelter microorganisms from disinfection or adsorb nutrients onto their surfaces which can sustain these organisms. This is of particular concern when ultra violet light is used as a disinfecting agent as the light may not be able to kill them.

Health effects
Although no health effects are directly related to turbidity which is a physical property of the water it is indirectly related to many potential ones e.g., aesthetic, corrosion, protection of pathogenic microorganisms from disinfection processes, provision of nutrients for pathogenic microorganisms and increase chlorine demand. The WHO recommend a operational maximum of 1 NTU at the final tap of a treatment works with a guideline value of 5 being objectionable to customers.

POLYCYCLIC AROMATIC HYDROCARBONS (PAH)
Benzo (a) Pyrene ug/l
Benzo (b) Fluoranthene ug/l
Benzo (ghi) Perylene ug/l
Benzo (k) Fluoranthene ug/l
Floranthene ug/l
Indo (123cd) Pyrene ug/l
Total Polycyclic Aromatic Hydrocarbons ug/l

These are a group of compounds, which consist of two or more benzene rings, which share two adjacent carbon rings.

From the last century to the mid 1970s in th U.K. most water distribution mains made of cast iron or ductile iron were given an internal anti-corrosion coating of coal tar pitch before being laid down in the ground. Coal tar pitch contains up to 50% of PAH and water supplied through mains lined with coal tar pitch has been found occasionally to contain PAH in suspension and in solution because of shedding of particulates containing PAHs and as PAH leachate. 

Health implications
It has been estimated food accounts for 99% of daily oral intake of PAHs with drinking water responsible for 0.1% of that total.

There are six indicator PAH compounds recommended by the WHO. Benzo(a)pyrene has caused stomach tumors in mice and has been give a guidevalue of 0.01ug/l from toxicity models which assume it is present along with other known PAH carcinogins. 

The other five indicators are listed above and have a guidevalue of 0.2ug/l. 

TRIHALOMETHANES (THM)
Chloroform ug/l
Bromoform ug/l
Bromodichloromethane ug/l
Dibromochloromethane ug/l
Total Trihalomethanes ug/l

THMs is a term used to describe a group of halogenated organic compounds derived from the halogenation of methane:

• Trichloromethane (Chloroform)
• Bromodichloromethane
• Dibromochloromethane
• Tribromomethane (Bromoform)
• Dichloroiodomethane
• Bromochloroiodomethane
• Chlrordiiodomethane
• Dibromoiodomethane
• Bromodiiodomethnae
• Triiodomethane (Iodoform)

They are of particular concern as they are suspected of being carcinogenic. a,b,c and d are the most commonly occurring. Technically fluorine is a halogen but can be discounted, as its occurrence in raw waters is very rare.

THM formation occurs by the chlorination of humic and fulvic acids which are derived from decay of vegetation in rivers. There is a natural fraction which has a strong seasonal input e.g., leaves and also that derived from sewage.

The use of granular activated carbon will remove THMs once they have been formed, although the ability of the media to do this decreases with time until it is regenerated. 

In the THM group chloroform is the most common constituent of the total value and is the one upon most toxicological study has been performed. 

Health implications
Chloroform is the most common THM formed and was used by the medical profession as an anaesthetic. Toxic effects of the other THMs are likely to be similar to that of chloroform.

It has been shown to be carcinogenic in laboratory animals subjected to acute high doses, but low level doses given to humans in drinking water as a result of water treatment are unlikely to ever reach such high values. 

A Guide value of 30ug/l for chloroform has been set by the WHO based on toxicity models. They make the point that the risk associated with inadequate disinfection is much higher than that associated with drinking water with THM values above the guide value. 

SOLVENTS
(a) Tetrachloromethane ug/l (Carbon Tetrachloride)
(b) Tetrachloroethene ug/l
(c) Trichloroethene ug/l

It is a synthetic chemical with no natural sources. It is used principally as an industrial solvent e.g., as a cleaning fluid, fire extinguishers, in the manufacture of chlorofluorocarbons "CFCs". It is of low solubility in water and persistent in the environment. 

Health implications
The evidence of carcinogenicity in several animal species (including man) is unequivocal. WHO have calculated a guideline value of 3 ug/l using a toxicity model. It can cause liver and kidney failure at acute levels, and gastrointestinal and nervous problems at a chronic level. 

PHENOLS
2,4,5-Trichlorophenol ug/l
2,4,6-Trichlorophenol ug/l
2,4-Dichlorophenol ug/l 
2,4-Dimethylphenol ug/l 
2,5-Dimethylphenol ug/l 
2,6-Dichlorophenol ug/l 
2-Chlorophenol ug/l 
2-Methyl phenol ug/l 
3,5-Dimethylphenol ug/l 
3-Methylphenol ug/l 
4-Chlorophenol ug/l 
4-Chloro-3-Methylphenol ug/l 
4-Methylphenol ug/l 

Phenols (total) ug/l 

Phenols can be defined as aromatic organic chemicals in which one or more of the hydrogen atoms has been replaced by a hydroxyl (OH) group. 

Phenols are likely to find their way into surface water sources as a result of pollution by trade waste, road washings etc. However phenolic substances do occur naturally in rivers by the degradation of humic substances and thus levels may rise after heavy rain an on a seasonal basis.

Phenols are used extensively in medicines, dyes, resins and as disinfectants e.g., TCP (trichlorophenol).

Health implications
Phenols are highly soluble in water. They are toxic compounds but consumption of phenolics at high doses in drinking water is unlikely since the taste threshold which would make the water undrinkable is well below the toxic level. 

It must be appreciated that a tasteless and odourless water will only guarantee that no toxic phenols or chlorphenols are present and is no guarantee of potability. 

During the river Dee incident adverse health effects were exhibited by some consumers exposed to levels of phenols above 3.5ug/l (US EPA guide level) for a short period.

Acute toxicity by phenol is characterised by a burning sensation in the mouth, sweating , abdominal pain decreased respiration and ultimately death from respiratory failure.

Chronic poisoning effects include, vomiting, anorexia, liver and kidney damage.

TOTAL ORGANIC CARBON (TOC) mg/l
This is a measure of both naturally occurring and synthetically produced carbon. It is a useful measure of the carbon loading at any point in the treatment process or in distribution.

Health implications
None directly.

HYDROCARBONS (dissolved) ug/l
Strictly these are compounds which contain carbon and hydrogen only. They may be aliphatic i.e., they have an open chain e.g., octane C8-H18 or they may be aromatic i.e., they have closed chain e.g., Benzene C6-H6. However the analytical test used by the laboratory will pick up alcohol, aldehydes, Keytones, acids, esters, alkyl halides, amines and amides as well, although discrimination between species is not possible.

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