Measurements

The E. coli bacterium is present in very high numbers in human or animal faeces and is rarely found in the absence of faecal pollution.  As such, its presence in drinking water is a good indication that either the source of the water has become contaminated or that the treatment process at the water treatment plant is not operating adequately. 

Enterococci

Enterococci originate in human or animal waste and thus their presence provides an indication that the water supply has been contaminated with faeces

Lead

Lead is present in drinking water primarily from its dissolution from lead pipes or lead-containing solder and thus the concentration of lead in drinking water depends on a number of factors including pH, temperature, water hardness and standing time of the water.  Consequently, the method of sampling for lead is critical and depending on the method used results can vary significantly.  According to the World Health Organisation (WHO, 2004) lead is a general toxicant that accumulates in bone.  Infants, children up to 6 years of age and pregnant women are the most susceptible to its health effects.  It is toxic to both the central and peripheral nervous systems.

Notes 3 and 4; Chemical Parameter

Nitrate

Nitrate in the environment originates mostly from organic and inorganic sources such as waste discharges, animal slurries and artificial fertiliser.  High levels of nitrate in drinking water may induce “blue baby” syndrome (methaemaglobinemia).  The nitrate converts to nitrite which reacts with blood haemoglobin thus reducing the availability of the blood to hold oxygen. 

Note 5; Chemical Parameter

Trihalomethanes – Total

Trihalomethanes (THMs) are derivatives of the simplest organic compound - methane, CH₄  - in which 3 of the hydrogen atoms are substituted by halogen atoms.  The principal halogens are fluorine (F₂), chlorine (Cl₂), bromine (Br₂) and iodine (I₂), but while many combinations are theoretically possible, the term trihalomethanes is applied to four specific compounds containing only chlorine and/or bromine as the halogen elements.  The four compounds are chloroform (CHCl₃), bromodichloromethane (CHBrCl₂), dibromochloromethane (CHBr₂Cl) and bromoform (CHBr₃). 

Chlorine (or appropriate compounds of it) is undoubtedly the most important chemical used in water treatment in Ireland today, as it has been in the past.  Although it is a highly poisonous gas in its pure form and a powerful oxidising agent, chlorine in very dilute solution is a most effective agent for the disinfection of water.  It is very efficient at destroying those bacteria which originate in human or animal waste and which cause undesirable and dangerous contamination of drinking water. 

As a powerful oxidising agent, chlorine also breaks down the complex and inert organic molecules which are the colouring agents of the water, forming smaller, reactive entities.  These entities react with chlorine (and with bromine derived from the oxidation by chlorine of bromide naturally present) to form the THM compounds, the most abundant of which is chloroform(CHCl₃).  There is thus a fairly straightforward relationship between the degree of colour in the water prior to chlorination and the quantities of THMs present following chlorination.  If colour is present at the point of chlorination, THMs are likely to be formed.

THM compounds are undesirable in drinking water for two reasons.  Firstly, the actual compounds themselves may pose a hazard to the health of the consumer if present in excessive amounts, as chloroform is a suspected carcinogen.  Secondly, the presence of the THM group may be an indicator of the possible presence of other organic by-products of chlorination in trace amounts. The WHO advises that “In controlling trihalomethanes, a multistep treatment system should be used to reduce organic trihalomethane precursors, and primary consideration should be given to ensuring that disinfection is never compromised”.compounds themselves may pose a hazard to the health of the consumer if present in excessive amounts, as chloroform is a suspected carcinogen.  Secondly, the presence of the THM group may be an indicator of the possible presence of other organic by-products of chlorination in trace amounts. The WHO advises that “In controlling trihalomethanes, a multistep treatment system should be used to reduce organic trihalomethane precursors, and primary consideration should be given to ensuring that disinfection is never compromised”.

Note 10; Chemical Parameter

Aluminium

Aluminium is present in drinking water as a result of its use as aluminium sulphate (a coagulant) in the water treatment process, though can be naturally present in some waters.  Historically, there has been some concern about possible links between aluminium in drinking water and Alzheimer’s disease.  However, the WHO states that:

“On the whole, the positive relationship between aluminium in drinking water and Alzheimer’s disease which was demonstrated in several epidemiological studies, cannot be totally discounted.  However, strong reservations about inferring a causal relationship are warranted in view of the failure of these studies to account for demonstrated confounding factors and for the total aluminium intake from all sources”.

Turbidity

The control of turbidity is one of the indicators of the efficiency of treatment at the plant.  Elevated levels of turbidity in the treated water indicate that the treatment process is not operating adequately.  It also provides a good indication of whether the treatment plant is capable of removing Cryptosporidium oocysts.  While the parametric value for turbidity (at the tap) is that the water must be “acceptable to consumers and [there must be] no abnormal change” there is a parametric value for turbidity (for water leaving the treatment plant) of 1.0 NTU.  However, it must be stressed that this value is for visual acceptability of the water.  In practice turbidity levels need to be much lower and should not exceed 0.2 NTU and preferably be below 0.1 NTU to be protective against Cryptosporidium breakthrough in the treatment plant.

Note 16; Indicator Parameter

There is no standard for Cryptosporidium in the Drinking Water Regulations.  Where Cryptosporidium is detected in a water supply the local authority should consult with the Health Service Executive in each specific case to determine whether there is a potential danger to human health.

(Source: EPA, 2009. The Provision and Quality of Drinking Water in Ireland - A Report for the Years 2007-2009.)

Monitoring of the Public Water Supplies in County Mayo is based upon a risk assessment method and the larger water treatment supplies are tested more regularly than the smaller water supplies. 

To date Mayo County Council have not detected Cryptosporidium in any of the water supplies tested.