Waterborne infectious diseases, in most emergencies, include diarrhoea, typhoid, cholera, dysentery and infectious hepatitis due to transmission of faecal pathogens, due to inadequate sanitation, hygiene and protection of water sources However, some disasters, including those involving damage to chemical and nuclear industrial installations, or involving volcanic activity, may create acute problems from chemical or radiological water pollution.
Whatever the source and type of contamination, decisions on acceptable water quality in emergencies involve balancing short- and long-term risks and benefits to health. At the same time, ensuring access to sufficient quantities of water is vital for health protection.
Many chemicals in drinking-water are of concern only after extended periods of exposure. Thus, it is advisable to supply water in an emergency, even if it significantly exceeds WHO guidelines for some chemical parameters, if the water can be treated to kill pathogens and then supplied rapidly to the affected population. This will reduce the risk of outbreaks of water-borne and water-washed disease. When water sources are likely to be used for long periods, chemical and radiological contaminants of more chronic health importance should be given greater attention. In some situations, this may entail adding treatment processes, or seeking alternative sources.
The principle of bacteriological testing is to identify a “faecal indicator” organism that is always excreted by warm-blooded animals, both healthy and unhealthy, and to take the degree of its presence as an indication of the degree of faecal contamination. Bacteria from the thermotolerant (faecal) coliform group are nearly always present in faeces, so their presence in water is a strong indication of faecal contamination. Typically, most thermotolerant coliforms are of the species Escherichia coli, which is always derived from faeces. The presence of any bacteria from the total coliform group is sometimes tested for, particularly as an indication of the effectiveness of a water-treatment system. Many members of the total coliform group are free-living and their presence does not depend on the presence of faecal contamination, but it can indicate that a treatment process has not removed or killed all bacteria. Other faecal indicator bacteria include faecal streptococci/ intestinal enterococci. Field kits for bacteriological testing usually employ the membrane-filtration technique, where a measured volume of water is filtered through a membrane, which retains the bacteria on its surface. The membrane is then incubated on a suitable medium, using a battery-powered incubator, for 18 hours. During this time, the thermotolerant coliform bacteria reproduce and form colonies. The number of colonies formed provides an index of the degree of faecal contamination in the original sample. This test is generally easy to perform. However, high turbidity caused by clay, algae, etc. (which may be suspended in large quantities after storms and floods) can interfere with the test, but as small volumes are often analysed in these circumstances, this may not be a significant problem. The multiple-tube method is an alternative to membrane-filtration. Quantities of the water to be tested are added to tubes containing a suitable liquid culture medium and incubated, typically for at least 24 hours. The bacteria present in the water reproduce, and the most probable number of bacteria present is determined statistically from the number of tubes giving a positive reaction (colour change and/or gas production). This test can accommodate even turbid samples, containing sewage, sewage sludge, or mud and soil particles.
Conventional bacteriological standards may be difficult to achieve in the immediate post-disaster period. The WHO guideline of zero E. coli per 100 ml of water should be the goal (World Health Organization, 1993a) and should be achievable even in emergencies, provided that chemical disinfection is employed. Recognizing that achieving the guideline standards may be difficult in some emergency situations, it is practical to classify water quality results according to the degree of health concern (Lloyd & Helmer, 1991; Delmas & Courvallet, 1994). For example:
— zero E. coli/100ml: guideline compliant;
— 1–10 E. coli/100ml: tolerable;
— 10–100 E. coli/100ml: requires treatment;
— greater than 100 E. coli/100ml: unsuitable for consumption without proper treatment.
An indication of a certain level of a faecal indicator bacteria alone is not a reliable guide to biological water quality. Some faecal pathogens, including many viruses and protozoa, may be more resistant to treatment (such as by chlorine) than the indicator bacteria. More generally, if a sanitary survey suggests the likelihood of faecal contamination, then even a very low level of contamination measured by bacteriological analysis may be considered to be a risk, especially during an outbreak of a disease like cholera that may be water-borne. The parameters most commonly measured to assess microbial safety are: E. coli (thermotolerant coliforms); residual chlorine; pH; and turbidity.
Chlorine content should be tested in the field with a colour comparator, generally used in the range of 0.2–1 mg/l of water. Taste does not give a reliable indication of chlorine concentration.
It is necessary to know the pH of water because more alkaline water requires a longer contact time or a higher free residual chlorine level at the end of the contact time for adequate disinfection (0.4–0.5 mg/l at pH 6–8, rising to 0.6mg/litre at pH 8–9, and may be ineffective above pH 9).
Turbidity, or cloudiness, is measured to determine what type and level of treatment is needed. It can be carried out with a simple turbidity tube that allows a direct reading in turbidity units (NTUs). Turbidity adversely affects the efficiency of disinfection
Chemical and radiological guidelines
Water from sources that are considered to have a significant risk of chemical or radiological contamination should be avoided, even as a temporary measure. In the long term, achieving WHO guidelines should be the aim of emergency water-supply programmes based on the progressive improvement of water quality.
Testing kits and laboratories
Portable testing kits allow the determination in the field of water pH (acidity/alkalinity), free residual chlorine, faecal coliform bacteria count, turbidity and filterability. When large numbers of water samples need testing, or a broad range of parameters is of interest, laboratory analysis is usually most appropriate. If laboratories at watertreatment works, environmental health offices and universities no longer function because of the disaster then a temporary laboratory may need to be set up. When samples are transported to laboratories, handling is important. Poor handling may lead to meaningless or misleading results. Workers should be trained in the correct procedures for collecting, labeling, packing and transporting samples, and for supplying supporting information from the sanitary survey to help interpret laboratory results.