Q2: What is pH?

The acidity or basic nature of water is expressed as the pH. It is important that the pH value be as close to 7.0 as possible in order to reduce the corrosivity of water and to limit its hardness and alkalinity. The regulations stipulate a range: 6.5 - 8.5 pH units. Interestingly, the toxicity of some substances in water can depend on the pH. For example, at a pH of 4.8, iron at 4.0 mg/L is not toxic to fish, however, if the pH is 5.5 then iron levels of 0.9 mg/L can cause fish kills. Some natural waters (where the soil is peaty) have pH values below or close to 6.0 with the result that pH adjustment will be required if the source is to be used for abstraction of drinking water. If the pH of water is low then it will cause corrosion to metal pipe work and introduce toxic metals into the supply. It is also important to realise that chlorine (rather hypochlorous acid) is a much more effective as a disinfectant if the pH is low. For instance at a pH of 8.0 the hypochlorous acid is present at 20% whereas at a pH of 7.0 the hypochlorous acid is now at 70% approx. Also, pH affects suspended solids removal from water. The lower the pH the better the flocculation will be and hence the filtration process will be more effective.

Q3: What is turbidity and what causes it?

Turbidity is a measure of how clear water is. The units of measure are NTU's (Nephelometric Turbidity Units). The lower the NTU of a sample of water the clearer the water is. The recommended value for drinking water: 0.5 NTU's. The higher the level of suspended solids in the water the higher the turbidity will be. The presence of pathogens such as Cryptosporidium and Giardia in surface water can cause turbidity and hence the need to maintain your supply at or below 0.5 NTU or less to protect your customers against these pathogens: for example, SI 439 of 2000 recommends that a maximum of 1 NTU "must be strived for".

Q4: What is chlorination and why is it necessary?

Common disinfectants are chlorine, ozone and UV. Chlorine is added to drinking water and leisure water in the form of chlorine gas, sodium hypochlorite, calcium hypochlorite or other Chlorine-containing disinfectants such as chlorine dioxide, to act as a germicide/biocide in order to remove harmful organisms such as bacteria, viruses, and cysts which may be in the water. As well as its effects as a germicide, chlorine will have other effects as well, causing insoluble oxides of iron and manganese to form in the water should the water contain soluble iron and manganese. In combination with organic material such as algal blooms, and especially with humic acid, trihalomethanes (THM'S) can also be formed: some of these are suspected carcinogens. Chlorine is not that effective in removing cysts from drinking water. Filtration is also needed.

The lower the pH and the higher the temperature of the water the more effective the disinfection power of chlorine disinfectants is. It is recommended that the residual chlorine in the distribution network be maintained at 0.1 to 0.3 mg/L chlorine as residual free chlorine. The effectiveness of the disinfection process is determined by a number of variables such as pH, water temperature, concentration of the chlorine injected, how good the mixing is, contact time and the amount of oxidizable matter present in the water. The World Health Organisation (WHO) has set as a guide level for effective chlorination, a residual free chlorine (RFC) value of 0.5 mg/L after 30 minutes contact. Viruses and cysts such as Cryptosporidium parvum, Giardia lamblia, Entamoeba histolytica, can be difficult to inactivate and it is therefore important to have effective contact time with the disinfectant so as to ensure protection of consumers at all times. Filtration is the most effective way of ensuring cysts do not enter the network.

Chlorination is effective if hypochlorous acid is present in the water and must be present as 'free chlorine' at points of use at about 0.20 mg/L as recommended by the World Health Organisation. The total chlorine can also be measured and the difference between 'free chlorine' and total chlorine indicates the level of pollution present prior to chlorination.

Health and Safety Issues:

Ingestion of sodium hypochlorite will burn the mouth and digestive tract. Sodium hypochlorite contact with the skin will also cause burns. Wear suitable personal protective equipment when handling chlorine disinfection products. Antidote: Bread-soda in water.

Note on the stability of sodium hypochlorite solutions: Sodium hypochlorite is available in solution form as 11%(w/v) sodium hypochlorite or 15% (w/v) sodium hypochlorite. These should be kept cool and in the dark. In sunlight these solutions will lose concentration at a rate of 3-4 percentage points per month. Even when held in the dark at 9 Celsius, the solution strength will drop by over 1 percentage point in a month.

Q5: What is Ozonation?

Ozone, a relative of oxygen, is also a powerful disinfectant. Its activity matches chlorine and essentially behaves in the same way, though there are no risks from THM formation with ozone as there is with the use of chlorine. The advantages are that the method removes taste and odour, improves palatability, oxidises iron, manganese, and organics, and is less sensitive to pH changes. It is also very effective against Cryptosporidium and as a disinfectant it is very powerful. The disadvantages are that it requires skilled maintenance input, it is expensive and unfortunately provides no disinfectant residual, thereby necessitating post treatment chlorination.

Q6: What is 'Blue Baby' Syndrome?

Nitrate derives from the oxidation of ammonia in the environment and also from agricultural nitrate fertiliser run-off. Drinking water contaminated with nitrate or nitrite can be hazardous to infants above 11.3 mg/L N(or 50 mg/LNO3-) giving rise to the so-called 'blue baby' syndrome (Methaemoglobinaemia). This condition has its origins in nitrite ingestion rather than nitrate. The nitrate is reduced in the body to nitrite, which in turn reacts with blood haemoglobin to induce the syndrome. The presence of nitrite in water sources above about 0.03mg/L indicates pollution. These parameters should be monitored regularly.

Q7: How do I know that the water is safe to drink?

There are several quality indicators of suitability for the purpose, broadly divided into two:

1. Chemical parameters:

The presence of heavy metals, ammonium, nitrate, aluminium, etc can indicate that the water is unsuitable for consumption. (See audit monitoring and check monitoring)

2. Biological:

a: General Coliforms: The presence of general coliforms in drinking water indicates that disinfection is not occurring or there is contamination post disinfection. These organisms are harmless: they merely indicate a potential problem.

b: E. Coli: Should E. coli be present in the water sample then there is an issue requiring urgent attention. In order to ensure that consumers are protected from hazardous micro-organisms such as E. coli 0157, a disinfectant such as chlorine or ozone must be added to water, usually following filtration, at about 2.0-4.0 mg/L. It is estimated that E. coli 0157 is present in 10-15% of the Irish cattle herd. The organism can be fatal if ingested.

c: Enterococci: The presence of these organisms again indicates that the source is contaminated with faecal material.

d: Cryptosporidium and Guardia must also be absent from drinking water. These are removed by filtration and chlorination.

Q8: How can I guarantee that my drinking water is safe?

There are no guarantees! All one can do is minimise risks to health.

1. Ask the water provider to present you with a copy of the water quality data obtained for the supply. Data for raw water as well as data for treated water would be of value.

2. A managed point of use treatment, is also a good way of ensuring that your water is meeting your requirements. There are a number of these systems available, from very simple treatment using particle filters to more sophisticated systems using reverse osmosis.

Reverse osmosis (RO) reduces significantly (normally >95%) the levels of contaminants, which may be in drinking water whether these are biological or chemical. As an indicator of the power of the technique, the conductivity of the water can be reduced significantly. The recommended arrangement is to use particle filters down to 1 micron in conjunction with carbon filters to further remove contaminants before the water is eventually passed through the RO membrane. Typically, total dissolved solids can be reduced from 200 mg/L to less than 20 mg/L when the process is applied. These are normally fitted under the sink in the kitchen and are easy to fit. The can provide up six purification stages. RO is very effective against cryptosporidium.

Q9: What is cryptosporidiosis?

Cryptosporidiosis is a diarrhoeal disease caused by microscopic parasites of the genus Cryptosporidium. Once an animal or person is infected, the parasite lives in the intestine and passes in the stool. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine-based disinfectants. Both the disease and the parasite are commonly known as "crypto." The parasite can be removed using reverse osmosis or by using filters which are 1 micron absolute. The parasite is not readily controlled by chlorine or ozone.

Q10: What are the symptoms of cryptosporidiosis?

The most common symptom of cryptosporidiosis is watery diarrhoea. Other symptoms include:

•    Dehydration
•    Weight loss
•    Stomach cramps or pain
•    Fever
•    Nausea
•    Vomiting
•  

Some people with crypto will have no symptoms at all. While the small intestine is the site most commonly affected, Cryptosporidium infections could possibly affect other areas of the digestive or the respiratory tract.