POU Water Purification in Emergencies

Water and sanitation (see also water supply and purification in emergencies and sanitation in emergencies(see PPT)) are critical determinants for survival immediately after and during the initial stages of a disaster (GWC 2009). Therefore, the availability of sufficient clean water in the immediate aftermath of a disaster is crucial in order to take care of the sick, to provide for human consumption to maintain basic hygiene, to support search and rescue efforts, and to ensure that productive and commercial activities get back to normal.

In case of an emergency, organisations may be present in camps or in some communities taking care of drinking water quality and wastewater treatment (see also camp water supply). If this is not the case, or if people remain in their homes, water has to be taken directly from water distribution networks (which may be damaged) or from existing water sources or brought in by water tankers by the government or relief organisations. These sources might be polluted or the population does not have good hygiene behaviour or no access to clean containers for collection and storage. In this situation, promoting Point-of-Use (POU) water treatment, sometimes also referred to as household-level water treatment and safe storage (HWTS), is an effective and relatively cheap option. POU water treatment techniques can easily be carried out after a brief and basic technical training (IFRC 2008).

POU water treatment as defined by the World Health Organization as HWTS consists of 4 steps: sedimentation); filtration (see also straining and filtration, ceramic candle filters, colloidal silver filters, or biosand filters); disinfection (e.g. chlorination, boiling, solar disinfection or UV-tubes); and safe storage. HWTS is a multi-barrier approach and is ideally combined with water source protection.

POU water treatment is often a temporary measure undertaken until the water source can be improved (IFRC 2008). However, the programmatic support (e.g. management and required awareness raising and training actions) required for POU water treatment may not be available in the initial phase of a disaster response when other higher priorities out-compete in the demand for time and resources (CLASEN & SMITH 2005).

It is important to note that securing appropriate water quantity in emergencies is prior to securing water quality at a safe drinking water level. Quantity is more related to water sources selection (availability, proximity and sustainability of sufficient water quantity, see also water sources), while quality further includes treatment, hygiene promotion (see also awareness raising (see PPT)) and all aspects of water safety plans (THE SPHERE PROJECT 2011).

Adapted from: OXFAM (2001)

Groundwater will predominantly be cleaner than surface water and will have less treatment requirements. Surface water sources in rural areas will probably need treatment to address high-suspended solids and to subsequently kill off microorganisms. Removal of the suspended solids presents the greatest treatment challenge, and technologies should thus secure sustainability in the medium- to long-term. Overly complex solutions should be avoided in general. The practice of sedimentation and use of aluminium sulphate as a coagulant is the most common procedure for this step in emergencies.

Before thinking of POU water treatment, the localisation and protection of water sources is of importance (see also water source protection). In case of emergencies, existing but damaged sources may be revived, new local sources of water may be made accessible (e.g. wells, boreholes, springs, streams, ponds or rainwater) or water may be taken from existing sources from neighbouring communities (REED & SHAW 1999; see also http://wedc.lboro.ac.uk/knowledge/notes_emergencies.html for some technical notes on how to clean wells and rehabilitate existing systems).

There are two types of water sources depending on their location: those situated above consumption points (provision of water by means of gravity; allow for systems with less operation and maintenance requirements) and those situated below consumption points (water system will rely on water lifting equipment). Ideally, the site should be chosen on the basis of the suitability of the water source, but the fact that sources situated above the setting are generally less exposed to contamination by poor hygiene practice and sanitation facilities should also be considered.

The available options and procedure correspond to the general HWTS approach methods as mentioned above, with slight changes according to the circumstances of the emergency:

Pre-treatment: Aeration

Aeration brings water in close contact with air, which increases the oxygen content of the water. This will: remove volatile substances such as hydrogen sulphide and methane which affect taste and odour; reduce the carbon dioxide content of the water; oxidise dissolved minerals such as iron and manganese so that they can be removed by sedimentation and filtration.

On a larger scale, aeration may be achieved by allowing water to trickle through one or more well-ventilated, perforated trays containing small stones. Again, the water must be collected in a container and allowed to stand for about 30 minutes to settle suspended particles before disinfection (KJAERGAARD et al. 2007). 

Sedimentation (see also sedimentation)

The main obstacle to the elimination of pathogenic organisms is high turbidity, as it prevents effective disinfection. If water is stored for a day in safe conditions, more than 50% of most bacteria die and suspended solids will settle to the bottom of the container. Households can maximise the benefits of storage and settlement by using the three-pot system (KAYAGA & REED 2011).

Suspended solids can be removed from water by mechanical or chemical sedimentation. This removal invariably presents the greatest treatment challenge and complex solutions should be avoided with regard to sustainability (OXFAM 2001). The chemical removal (e.g. by using Watermaker or PUR, see IFRC 2008) is especially useful in floods since turbidity is effectively removed and water disinfected. But the flocculent/coagulation and disinfection method is significantly more expensive compared to single chemical disinfection of non-turbid raw fresh water (IFRC 2008).

Alternatively, roughing filters can be applied as pre-filters to treat water of high turbidity (>50 NTU). They speed up the settlement process significantly, because particles are removed by both filtration and gravity settling. Roughing filters improve the solid removal efficiency without the use of chemicals (EAWAG 2011; OXFAM 2001; WEGELIN 1996).

Filtration

A common filtration method proposed in emergency situations is straining by pouring water through a piece of clean fabric, straining removes some of the suspended solids and is therefore an improvement for people with no other options. Filters such as ceramic filters, colloidal silver filters, and biosand filters are not commonly used in emergencies (IFRC 2008) but can be an option in some cases. In the 2004 tsunami response, Oxfam decided to deploy ceramic filters and biosand filters only in the resettlement phase when people began to re-establish their households more permanently (CLASEN & SMITH 2005). As an example of a natural filtration system, infiltration wells close to water streams will usually provide better-quality water than the water stream itself (see also river bank filtration). The sand and gravel deposited beside and below a river act as an effective water filter (REED & SHAW 1999).

Disinfection

Disinfection is used to destroy pathogenic organisms. In non-emergency situations, certain waters may not require disinfection (e.g. deep groundwater, mountain streams). However, disinfection should be used wherever possible in emergencies as an added precaution (HOUSE & REED 2004). The traditional method of boiling can provide safe drinking water in emergencies (except at high altitudes), however, it requires a lot of energy (e.g. fuel, which might be scarce) and does not remove turbidity or chemical pollution (e.g. arsenic).

The most common (chemical) disinfection method is through chlorination. When used correctly, chlorine will kill all viruses and bacteria, but some species of protozoa and helminths are resistant to chlorine. Some of the chlorine compound should remain in the water to increase the likelihood that the water will remain safe to drink during storage (KAYAGA & REED 2011; REED & SHAW 1999; WISNER & ADAMS 2002). Solar water disinfection or SODIS can be achieved by exposing fresh water to solar light (UV-A radiation) for at least six hours. It can remove bacteria, viruses and some parasites, but not chemical pollution e.g. arsenic, fluoride or agricultural residues. SODIS by using transparent PET bottles is extremely low-cost and simple. UV light is also efficient in killing most microorganisms (see also uv tubes).

Safe Water Storage

Safe storage means keeping treated water away from sources of contamination, and using a clean and covered container. It also means that water should be drunk from the container in a way that people do not make each other sick (CAWST 2009). On refugee sites, storage facilities are required in the distribution system as well as at household level (UNHCR 2007).

The 2004 earthquake and tsunami in the Indian Ocean affected coastal areas’ water supply systems. Relief organisations encouraged the affected population to treat their own water, mainly by boiling. In other areas chlorination was done with bleach (sodium hypochlorite), bleaching powder (calcium hypochlorite), chlorine tablets (NaDCC, halazone). Also PUR sachets (combined flocculent and disinfectant), and alum (flocculent) were distributed for treating water at the distribution points (see camp or community water supply) or at the household level via sedimentation. Relief organisations also began distributing vessels and utensils for collecting, storing and consuming water (CLASEN & SMITH 2005).

The limited role of household water treatment was not a result of unavailability of the technology. In fact, the quantity of products sent to the region for the purpose of treating water was remarkable. The five main reasons for not using household (POU) water treatment in the tsunami emergency response have been identified as follows (CLASEN & SMITH 2005):

• Emphasis on water quantity over quality, since physiological needs (hydration) outweigh microbiological concerns
• Bulk supply of water made POU water treatment unnecessary: the affected population was either displaced or had otherwise lost access to their customary sources of fresh water. Hence, they were dependent on water supplied in bulk.
• POU water treatment measures require programmatic support to induce behavioural change (chlorination, solar disinfection)
• Concern over conflicting messages being given to the affected populations, resulting in a decrease of normal practice (e.g. boiling in Aceh), thus leaving individuals exposed to increased risk of waterborne diseases
• Concern over sustainability of newly introduced and promoted POU water treatment methods. Short-term behaviour change without sustained promotion could be detrimental to health if it means the abandonment of previous safe drinking water practices.

Although POU approaches to water treatment have proven to be effective in development programmes, their utility in emergencies has not yet been widely demonstrated. During the immediate emergency phase, the evidence from the first three months following the 2004 Indian Ocean tsunami suggests that household water treatment may be inappropriate after a disaster of this kind (CLASEN & SMITH 2005).