Preventing Recontamination

Most drinking water around the world, from almost every water source, should be considered unsafe (see also pathogens and contaminants) unless it is treated and stored properly. Even where piped water is delivered to the household, point-of-use treatment by boiling or other methods is widespread—and for good reason. Intermittent service, degraded infrastructure, or unreliable water treatment forces many people to question the quality of water they drink. Increasing scarcity of high-quality water has led to significant and growing demand for products and services that provide safer drinking water, particularly in the developing world, where water supply infrastructure has not kept pace with economic growth and population shifts (BROWN et al. n.y.).

The principal health risk (see also health risk management) associated with household water storage is the ease of recontamination during transport and storage, particularly where the members of a family or community do not all follow good hygiene practices. The most crucial factor for preventing recontamination or regrowth at the household level is safe storage. In the case the risk of recontamination or regrowth is high, residual point-of use water purification, e.g. chlorination is required. After the purification, water should be tested before it is consumed (adapted from WHO (1997)).

Below, there is a description about common processes and problems in piped distribution systems and how to prevent them.

Microbiological growth and regrowth

The threat of excessive microbial growth along the interior walls of drinking water distribution pipes is a common problem. The development of an organic bacterial community, also commonly known as biofilm, is composed of microorganisms and their secretions. It is present in almost every water distribution system, and when uncontrolled may present a threat to public health.

Chlorination: Chlorinating the drinking water supply (residual chlorination) is the method usually used to control biofilm growth. In most cases, maintaining the normal amount of chlorine used to disinfect drinking water will control this problem (WQHC 2012).

Chlorine Residual Testing: The presence of residual chlorine concentrations in drinking water indicates that (CDC n.y.):

• A sufficient amount of chlorine was added initially to the water to inactivate the bacteria and some viruses that cause diarrhoeal disease.
• That the water is protected from recontamination during storage. The presence of free residual chlorine in drinking water is correlated with the absence of disease-causing organisms, and thus is a measure of the potability of water.

According to WHO guidelines, the FRC (Free Residual Chlorine) concentration in drinking water should be between 0.2 to 0.5 mg/L (WHO 2006). Read more about it in the factsheet about centralised chlorination.

Permeation

Permeation in water distribution systems occurs when contaminants external to the pipe materials and non-metallic joints pass through these materials into the drinking water. Permeation is generally associated with plastic non-metallic pipes (see also water distribution pipes). The contaminants that are most commonly found to permeate plastic pipes are organic chemicals that are lipophilic and non-polar, such as highly volatile hydrocarbons and organic solvents, because they can readily diffuse through the plastic pipe matrix, alter the plastic material, and migrate into the water within the pipe (NATIONAL RESEARCH COUNCIL 2006). But also the intrusion of polluted groundwater or leakages from sewer systems can cause recontamination (see also leakage control). This is particularly a problem when intermittent water supply is common.

Leaching

All materials in the water distribution system undergo reactions that introduce substances to the water via a process known as "leaching." Pipes, fittings, linings, and other materials used in joining or sealing pipes leach at least some substances to water through corrosion, dissolution, diffusion, or detachment. Internal coatings in water storage facilities can also leach substances. Most known substances that leach into water from materials in the distribution system do not appear to pose a public health threat due the fact they are non-toxic, present only at trace levels, or are in a form unlikely to cause health problems. However, taste and odour complaints are possible (NATIONAL RESEARCH COUNCIL 2006).

To prevent leaching as well as permeation problems, operation and maintenance of drinking water networks (see also leakage control) and sewer lines is important, as well as groundwater and soil quality.

Lead poisoning

Exposure to lead causes a variety of health effects, and affects children in particular. Water is rarely an important source of lead exposure except where lead pipes, for instance in old buildings, are common (see also water distribution pipes). Removal of old pipes is costly but the most effective measure to reduce lead exposure from water (WHO 1993).

To prevent recontamination in large distribution systems, qualified labourers, technical equipment and an organised management are needed. These raise costs for such a system but prevent health costs.