Safe Storage

Already treated or purified water has to be stored properly to prevent recontamination. Safe storage means keeping your treated water away from sources of contamination, and using a clean and covered container. It also means that drinking from the container should be done in a way that cross-contamination can be avoided. The container should prevent hands, cups and dippers from touching the water, so that the water does not get recontaminated (CAWST 2009). There are several possibilities to store water. They range from very small covered buckets to large tanks or cisterns. Another possibility is to store water in bottles. Furthermore, the hygienic conditions in a household are crucial. Good hygienic measures include the following (WHO 1997):

• Careful storage of household water and regular cleaning of all household water-storage facilities.
• Construction, proper use, and maintenance of latrines.
• Regular hand washing, especially after defecation and before eating, preparing food or handling drinking water.
• Careful storage and preparation of water and food.

Treated water should be stored in plastic, ceramic, or metal containers especially when using treatment options that do not leave residual protection. The following characteristics of containers serve as physical barriers to recontamination (CDC & U.S. AID 2009):

• A small opening with a lid or cover that discourages users from placing potentially contaminated items such as hands, cups, or ladles into the stored water.
• A spigot or small opening to allow easy and safe access to the water without requiring the insertion of hands or objects into the container.
• A size appropriate for the household water treatment method, with permanently attached instructions for using the treatment method and for cleaning the container.

The following aspects should be considered when planning for safe storage and prevention of recontamination (WHO 1997):

• Location of storage vessel
• Design of storage vessel
• Removal of water

Small-scale storage

The Oxfam bucket

The 14-litre Oxfam Bucket was designed to provide a safe storage option to organisations working on water safety in the home or refugee camps. It is manufactured in England, and sold unassembled to NGOs for use in programme implementation. The lids snap on to prevent entry of the hands or objects into the container. The Oxfam Bucket costs about US$11 (CDC & U.S. AID 2009; OXFAM 2012).

The CDC SWS container

In the initial Safe Water System (SWS) programmes, the CDC designed 20-litre modified jerry cans and provided them to users. This jerry can is now produced in Uganda, Afghanistan, Kenya, and the United States. Each jerry can costs approximately US$5, excluding transport (CDC 2012).

Jerry cans

In many countries in Africa, 20-litre jerry cans, initially used to transport vegetable cooking oils, are cleaned and used to transport and store water. They are easy to carry on the head (see also human powered distribution) and are a good option for safe storage. The opening is too small to allow hands or utensils into the water; instead the water is removed by pouring. Drilling a hole in the plastic and adding a tap provides easier access to the treated water and allows for a hand-washing station in the home. Used jerry cans cost approximately US$1-5 on the market in Africa (CDC & U.S. AID 2009).

Bucket with lid and tap

Five gallon (19-litre) buckets are widely available in many countries and are often used for water transport and storage. Buckets can be modified for safe storage by ensuring the installation of a tight-fitting lid, or by drilling a hole through the plastic and installing a sturdy tap. Furthermore, a label with instructions for water treatment should be placed on the bucket, and people should be instructed to use the tap instead of dipping into the bucket. In Haiti, this is an easy educational message, since the tap is seen as a sign of higher socio-economic status, and families take pride in using it. Taps and labels can be imported or locally made (CDC & U.S. AID 2009).

  Modified clay pots

In many cultures, clay pots are the preferred storage container, because the water inside the container is cooled as water evaporates through the clay. In some rural areas, water is transported in clay pots, but in most areas water is transported in plastic containers and then stored in clay pots. By working with local potters, it is possible to modify clay pots to have a tap and an adequate cover, as seen in the two examples (CDC & U.S. AID 2009).

The Q-drum

In impoverished rural areas, clean water is often miles away from the people who need it, leaving them susceptible to waterborne diseases. The sturdy Q drum holds around 50 litres in a rolling container that eases the burden of transporting safe, potable water. One unit costs about US$60 (QDRUM 2011; VEGAS 2011). Also read the factsheet human powered distribution.

Large-scale storage

Large storage plastic tanks

For settlements in rural areas, large storage tanks are a possible solution if there is no connection to a water distribution network. They are either filled by tank trucks or by a rain water harvesting system. Plastic tanks are available in all sizes, from small to very large. It should be considered that they are UV stabilised, durable and impact resistant, impervious and made out of non-toxic material (e.g. food grade approved polyethylene) (PRACTICAL PLASTICS n.y.). Costs depend on manufacturer, country and size. The water in storage tanks should be tested regularly (UNHCR 2007).

Cisterns

Adapted from ALI et al. (2009)

Two types of cisterns are common: single-cell and multi-cell. The choice of single or multiple cells depends on the rock and soil characteristics and the storage requirements. Cisterns of larger capacity (>300 m³) generally have more than one cell, while single-cell cisterns are smaller, usually built where soil and rock conditions do not allow for large capacity. A cistern has three main components: an inlet including a settling basin, a shaft (mouth and neck), and a storage chamber. The inlet allows runoff to enter the storage chamber, while the outlet allows excess water to flow out. The mouth opening facilitates withdrawal of water from the cistern, and is 50-75 cm in diameter. A wooden or steel grate covers the opening to prevent the entry of contaminants. The chamber is excavated in soft to medium soils underneath a layer of hard sedimentary rock, 0.5 metres to 2 metres thick, which forms a natural ceiling to the chamber. The inner sides of the chamber are plastered to minimise leakage. The chamber requires cleaning every four to five years if proper sediment traps are not provided. Generally, water is extracted from the cistern using buckets, although windmills, hand pumps or mechanised pumps are also used.

User experience shows that accumulated sediment must be removed from the cistern every 4 to 5 years, which adds to recurring maintenance costs. Soil erosion and debris/log flows from the catchment are the main sources of sediment. Flow concentration by water harvesting can increase sediment entry into the cistern. Steep slopes and weak soil structure in the catchment area also increase sediment production. Vegetation cover in the catchment area can reduce sediment, but also reduces runoff and may reduce water quality below drinking standard as shown in the factsheet on purification. Sediment can be reduced by treating problem spots in the catchments through compaction of loose patches, treatment with impermeable membranes, and breaking the steep land slopes. A sediment-settling basin immediately upstream of the entry point can significantly reduce sediment inflow. Furthermore, cisterns for domestic use and animals are separated from those for agriculture.

Towers

Adapted from BHARDWAJ & METZGAR (2001)

Water towers can be made of concrete or steel and can take various forms. The most suitable form for concrete towers is a cylinder with a curved shaped bottom or with a flat bottom. Steel tanks may have a spherical or dome shaped bottom. The shape chosen is usually a compromise between function, construction and maintenance costs, as well as aesthetics. The lowest water level in the tank is determined according to the pressure requirements in the pipeline. The pressure in the pipelines may vary depending on the type of community and pressure needs of different areas in a city. To keep pumping costs low, water depth in the tank is generally kept small. Due to structural considerations, the depth is kept equal to the diameter.

The costs depend on the used storage system. Small-scale storage such as covered buckets or clay pots (see description above) can be very cheap. Large-scale methods, such as tanks, towers or cisterns need more technical supply and know-how (design, construction, material, pumps, etc.) and are very often owned by communities.

Storage for domestic and animal use and agricultural use must be strictly separated. An outlet such as a tap or a piping system should always be appropriately designed to prevent contact with hands or other sources of contamination, thus pouring treated water from the container rather than scooping the water out of it. Tanks, buckets or other storage types must be cleaned and flushed regularly to prevent health risks and recontamination. Purified water at household level should be used as soon as possible, preferably the same day, to minimise the risk of recontamination (CAWST 2009). In general, water from sources such as reservoirs, rainwater tanks, covered buckets or other water sources must be -purified before used as drinking water. It is also highly important to wash hands regularly, especially after defecation and before eating, preparing food and handling drinking water (WHO 1997).

All the described storage accessories must be cleaned and inspected regularly. Biofilm, sedimentation, cracks, missing coverage, etc. are problems that might lead to a degeneration of water quality. Cleaning of storage tanks is especially important, if it held other contents before. This could be the case in an emergency (read more about this in GODFREY and REED 2011). The stored water should be tested regularly to ensure its quality.