3.3.1 Quantity and quality
The most likely source of cholera transmission during an outbreak is water (used for drinking or food preparation) contaminated with faecal matter. Water may be contaminated at the point of access (river, well, municipal system, water vendors, etc.), during transport or at home, in storage containers.
Outbreaks often start after a failure in the water distribution system has forced people to use non-protected water sources (rivers, ditches, polluted wells). Poor access to water in sufficient quantity negatively affects hygiene practices, leading to the spread of cholera.
It is therefore essential to provide people with safe water in adequate quantity by repairing existing distribution systems or setting up temporary supply solutions.
At least 15 to 20 litres of potable water should be provided per person and per day1
for drinking, cooking and hygiene (personal and domestic).
During a cholera outbreak however, water needs increase (more frequent hand washing, laundry and cleaning of surfaces; ORS preparation, etc.). It is recommended to provide as much water as people need, also taking into account other factors such as hot climate, cultural practices (e.g. water for ablutions), etc.
There are no widely available rapid tests to detect and quantify Vibrio cholerae in water.
Common indicators, such as pH, turbidity, free residual chlorine (FRC) concentration and if available, presence of Escherichia coli2 , provide an indication of the quality of water and if treatment is needed. For test techniques, see Appendix 17.
3.3.2 Water chlorination for public distribution
Water chlorination is the best means to quickly provide large amounts of potable water.
Chlorine-generating products are widely available and the water remains protected during transport or storage by the presence of FRC. A high level of FRC at the point of delivery is essential to guarantee the water is potable and protected against recontamination during storage for 4 to 24 hours2. However, users may dislike drinking water with a strong smell or taste of chlorine. An information campaign may be necessary to increase acceptability.
Table 3.1 - Conditions for effective chlorination against Vibrio cholerae
< 5 NTU* (Sphere Project standard), nevertheless, during the initial stages of an emergency, turbidity < 20 NTU is acceptable.
• 30 minutes if pH ≤ 8
At all distribution points (taps, standpipes, tanker trucks, etc.) and in recipients if bucket chlorination :
* NTU = nephelometric turbidity unit
If turbidity is over 20 NTU (emergency situation) or 5 NTU (other context), the water needs to be treated to reduce turbidity before chlorination. For techniques (sedimentation, filtration), see Public health engineering in precarious situations, MSF.
In line chlorination
Where there is a functional water distribution network but water is poorly, insufficiently or not at all disinfected, determine the causes of the problem (e.g. shortage of chlorine, malfunction of chlorination system, chlorination protocol not respected) in order to remedy it.
The supply of chlorine and other chemicals3 should be well organized to guarantee a constant production of potable water, at least for the duration of the outbreak.
Where there is no water distribution network, water can be collected at central filling stations and transported, by water truck (or other vehicles equipped with a reservoir), to the distribution point.
Filling stations either pre-exist or are set up for the needs of the operation.
Once transported to the distribution point, the water is transferred into one or more water bladders to be distributed.
The water must be chlorinated before distribution. It can be chlorinated either:
– directly at the source (the water collected is already chlorinated),
– while filling the water truck,
– while filling the water bladder at the distribution point.
Distribution points should be located so as to provide everyone affected by the outbreak with access to clean water.
When chlorinating water in trucks or bladders, the water should be tested to determine the quantity of chlorine required to disinfect the volume of water in the truck or bladder. As the volume of water remains constant, the amount of chlorine to be added to the truck or bladder will be the same at each collection, provided the quality of the water does not change. A trained person, e.g. the truck driver, is responsible for chlorinating the water.
Bucket chlorination is usually implemented when in line or batch chlorination is not available or feasible.
Water intended for human consumption is collected by the population from an unprotected or contaminated source (e.g. open well, river) and disinfected directly in the jerrycan or bucket by a trained person (a chlorinator) stationed at the source. Once the container is filled with water, the chlorinator adds the appropriate amount of chlorine solution according to the volume of the container4 .
The population may have the choice between several sources used for different purposes (drinking, cooking, laundry, bathing). Priority is given to sources used for drinking and cooking, and identified as being contaminated or at the origin of point source or continuous outbreaks5 .
Since one chlorinator is needed per source, a limited number of sources should be selected with local authorities: the most accessible, which can be treated effectively (pH, turbidity).
Ensure constant chlorine supply to all sites and proper supervision by experienced staff, who regularly visit each site, ensure the protocol is respected and check the level of FRC.
Note: direct chlorination of wells and other unprotected sources is not recommended as it is ineffective.
Water quality, whatever the chlorination system used, must be routinely monitored throughout the outbreak.
For more information on treatment methods, see Public health engineering in precarious situations, MSF.
3.3.3 Household water treatment and storage
There are different products, each designed to treat a specific volume of water.
– Chlorine generating products:
These can only be used with clear water (i.e. turbidity < 5 NTU; < 20 NTU in extreme emergencies).
• Tablets of sodium dichloroisocyanurate (NaDCC )
• Solutions of sodium hypochlorite (bleach)
As for all chlorination measures, the efficacy of the product (level of FRC) must be checked before each distribution and regularly throughout the operation.
– Products combining flocculent(s) and disinfectant:
These are designed for use in water with over 5 NTU. It is recommended to test them as they are not always effective in removing all particles or generating a high enough level of FRC. These products require more than one container and several steps (mixing, waiting and filtering) to produce clear and disinfected water.
– Boiling water:
Heating water to a rolling boil, and keeping it boiling for 1 minute, kills bacteria. However, it is not the preferred method (difficult to implement especially in emergency, requires a lot of energy) unless it has been promoted for a long time in the area by local authorities or if no other solution exists.
– Water filtration:
There are many household filtration systems. Their ability to remove Vibrio cholerae depends on the system itself, but mainly on the use and maintenance once in the home.
Boiled or filtered water is more easily re-contaminated than chlorinated water.
Household water storage
Receptacles without lids or with a wide opening increase the risk of contamination. Potable water must be stored in containers with a narrow neck or with a tap. These containers must be regularly cleaned.
Boiled or filtered water or water from a non-contaminated source that has not been chlorinated must be chlorinated at household level if intended to be stored. Contamination of water during household storage is common and the presence of FRC in water prevents (re)contamination.
Household training and surveillance
It is essential to carry out training sessions for households either before or during the first distribution of chemical water disinfectants or household water filters. The training sessions must also include information on water storage.
Afterwards it is important to regularly check the effectiveness as well as the correct and constant use of the products or filters.
The Sphere project recommends 15 litres (minimum quantity of water to survive), the WHO a minimum of 20 litres.
When water is not chlorinated, E. coli count should not exceed 10 CFU (colony-forming units) per 100 ml. The presence of a greater number of E. coli indicates the water is contaminated with faecal matter, but is not proof of the presence of Vibrio cholerae or any other pathogen.
Products for the pre-treatment of water before chlorination (e.g. coagulants such as aluminium sulfate).
Other water treatment products (e.g. tablets of NaDCC, see Section 3.3.3) can be used instead of a traditional chlorine solution to simplify the process or as a step prior to general distribution so that users learn how to use it and adopt the product.
In point source outbreaks the population at risk is exposed to Vibrio cholerae at the same time within a short period. In continuous source outbreaks, exposure is prolonged over an extended period of time.