Water storage is essential for areas where there is no supply infrastructure or there is unreliability. It is cost effective where water needs to be purchased. The NWSC bills 0.96 USD per 1,000L of water for institutions. This price is higher in rural locations where water is collected and transported from public taps at 0.14-0.27 USD for a 20L jerry can. A typical classroom block without an alternative water supply requires 25,000-30,000L of water storage, while two classroom blocks require in the region of 40,000-50,000L. This capacity can be contained in a single big tank or multiple smaller tanks, depending on preference.
Tanks built of curved corrugated iron sheets welded into cylindrical tanks are the cheapest but least durable water storage option.
Capacity - 2,000L - 15,000L
Life span - 7 years
Cost (10,000L) - $550
Corrugated iron tanks were one of the earliest rainwater storage options available and continue to be cheaper than any alternative. They are generally not sold at hardware stores, but at specialized metalworks where fabricators weld 24 or 26 gauge iron sheets together to form cylindrical water tanks. The tanks rust quite quickly and can only be expected to last in the region of 7 years. They are far more common in households than in schools, as institutions generally opt for greater durability.
A corrugated iron water tank showing signs of rust
The most expensive water storage option: stainless steel tanks are more durable than any alternative, which can result in cost savings in the long-run. They are quick to install and more robust to receive plumbing than plastic tanks. Furthermore, stainless steel is unaffected by intense heat conditions and does not support the growth of bacteria or algae, making it a hygienic option for water storage. It is also recyclable in nature, so is arguably one of the more eco-friendly options.
Capacity - 750L - 500,000L
Life span - 50 years
Cost (10,000L) - $2,200
Stainless steel tanks are by far the most expensive option but are rust and corrosion resistant and durability may result in cost savings in the long run.
Plastic water tanks are the most common water storage option for schools. They have decent durability but can be vulnerable to vandalism
Capacity - 100L - 24,000L
Life span - 20 years
Cost (10,000L) - $1,300
In many ways plastic tanks are the standard solution although they are relatively expensive and limited in capacity to around 24,000L. They are often organised in multiple tank systems, and should be placed at the same level and interconnected via underground popes so that they function as one big tank. Plastic tanks are vulnerable to vandalism and cal also become damaged through prolonged exposure to UV. They can require the construction of a protective brick wall, or shading elements, such as bamboo or planted screening, which further pushes up cost.
NTC Kaliro Two large plastic tanks at the end of each of the buildings are screened with bamboo to protect them from direct sunlight.
Underground water tanks are often a preferred option as they can be constructed from local materials are cost effective, secure and discrete.
Capacity - 5,000L - 200,000L
Life span - 25 years
Cost (10,000L) - $1,050
Underground water tanks offer a discrete and space-saving storage solution. The surrounding earth creates external resistance to water pressure, which means that costly reinforcement can be reduced. Tanks may be rectilinear or domed with a reinforced concrete slab. A masonry structure, usually fired brick is finished with a waterproof cement plaster. The exterior is painted with bituminous paint. Water must be fetched via a pump, which may be manually operated, fuel, mains or solar powered. An access point for the pump is all that is visible above ground
Interlocking stabilized soil blocks offer a low cost, but labour intensive solution to water storage. ISSB tanks are well protected against damage and theft.
Capacity - 5,000L - 200,000L
Life span - 15 years
Cost (10,000L) - $990
ISSB tanks are extremely versatile and can be built above or below ground in a wide range of sizes from 5,000L - 200,000L capacity. Smaller tanks require a specialist press that produces a curved ISSB block, whereas large tank sizes can be produced with regular straight blocks. No reinforcement is required for tanks of 50,000L or less. Above this is a double ISSB wall is recommended, consisting of two concentric circles with cement mortar packed between them. ISSB tanks are cost effective and environmentally friendly, but are labour intensive to construct.
A large ISSB water tank consisting of two concentric circles of standard ISSB for additional reinforcement.