Frequently asked questions

1 part cement to 3 parts sand.

An advantage of cement tanks is that they can be easily repaired. In fact minor leaks often self-seal with fine particles that leach out of the cement.

For smaller repairs simply mix some cement with water and apply to the crack on the inside face after emptying the water.

For larger cracks, again drain the water, then open up the crack to make the gap big enough for mortar to fill. Make a 1:2 mix of cement: sand, make the rough surfaces damp and work a fairly dry paste well into the gap.

We’d love to know the answer to that too, particularly in relation to other solutions like plastic tanks or pipework distribution to households. If you have an answer, let us know!

In Africa, only 39% of the population used safely managed drinking water as of 2020. The most affected region is Sub-Saharan Africa, where around 794 million people lack clean drinking water. UNICEF estimates it would need to increase its efforts 12-fold in order to achieve the Sustainable Development Goals (SDGs) by 2030.(source: World Economic Forum). There is a government push towards rainwater harvesting in many countries as a means of reducing demand on municipal water infrastructure. This is fed, in part, by the UN’s Sustainable Development Goals (Goal 6A) that promote rainwater harvesting (RWH).

CED is building rainwater tanks for some of the poorest people in Tanzania. The water security provided makes a huge difference to the quality of life of the recipients. One recipient described the difference: “Before we had a tank my days were consumed fetching water. If I decided to go to get water, that was my day – nothing else got done. The tank changed our lives. I can now focus on other things like taking care of my hearing and sight impaired husband and disabled daughter. The tank didn’t just provide convenience, it brought a profound sense of security and freedom. Thank you so much for empowering our community. Having this tank hasn’t just changed our lives – it has improved the lives of everyone around us”

1. The technology is proven over many years.
2. Tanks are robust and last indefinitely.
3. Rainwater stored in tanks remains fresh and can be drunk with little risk, though we recommend boiling or “SODIS” treatment for children.
4. The water remains cool.
5. Local partners appreciate that ferro-cement technology creates local jobs and keeps money in the community rather than going to corporations elsewhere as with plastic tanks.
6. Owners appreciate the robustness of ferrocement.
7. In most instances the cost of a ferrocement tank is less than that for a plastic tank. The difference is more marked away from major centres where there are plastic tank factories.
8. In remote locations it is easier to transport materials (e.g. by bicycle) than to transport a completed tank.
9. There is an emerging middle class in most towns who are looking for better ways to store water.
10. Climate change means that water supplies are more erratic so that storage is becoming more important.
11. Aquafers are being exhausted near urban areas due to over-extraction, forcing people to look elsewhere.
12. Increasing population density is putting pressure on municipal piped water supplies; authorities are encouraging people to collect rainwater to reduce pressure on over-stretched systems.

We regret that this would not be desirable. There are various risks around exploiting vulnerable people, building dependency, etc. However, if you’d like to visit the programme we could introduce you to families who have built tanks and show you how they are made. This could be done in the context of the CED manager visiting the project and you would meet our partners and also some tank owners. Please contact CED to discuss.

The rate fluctuates around 3,300 – 3,400 Tsh/£.

This varies depending on location. As well as materials costs and labour charges, there are logistics costs and supervision costs to consider. For this reason, although we estimate a 1000 litre tank to cost around 370,000 Tsh, CED grants 460,000 to our partner to include overheads when the tank is being given to a vulnerable person.

A 5,000 litre tank is estimated to cost 1,200,000 Tsh. CED offers a grant of 1,000,000 Tsh to institutions like churches and schools.

A 10,000 litre tank is estimated to cost 1,700,000 Tsh. CED offers a grant of 1,500,000 Tsh to institutions like churches and schools.

CED supports partners to develop their own rainwater harvesting projects. They do this by training local masons chosen by the partner then offering grants towards the cost of tanks.

The programme is modelled on a “franchise” approach (c.f. McDonalds hamburgers).

For CED’s Rainwater Harvesting (RWH) programme, CED (franchisor) provides ongoing support by visiting the overseas partner (franchisee) and discussing problems, checking on quality of tank building, developing “best practice” and providing ongoing financial incentives. The partner (franchisee) follows the proven business model, reports on spending of CED funds and develops its project to meet the needs of those it is serving.

CED is keen to partner with organisations that already have a presence in village communities. On its own, the provision of a tank is unlikely to transform lives. It is when the tank is part of a broader community initiative, perhaps social or spiritual, that it is likely to be most appreciated. The cost of supervision of building is much reduced if the partner is already visiting the village for other reasons.

The partner chooses people for training. Group size should be between 12 and 20 students. There should ideally be one or two female students and most students should have masonry skills. If two or three students come from the same village they will be able to build tanks when they return home.

CED seeks out the most marginalised in a village, relying on church personnel to know the circumstances of people.

Such people may be widows, or younger single parents with more responsibilities than they can cope with, or people who have a debilitating illness.

Households that have a municipal (piped) water supply are not be considered for support.

Until the truly marginalised have their meets met, CED does not wish to support people with a good family network to support them, or people who are generally managing as they are. Such people are encouraged to save and purchase a tank, with a grant from CED.

• The partner sends a list of proposed tanks to CED with names of recipients.
• CED sends a lump sum based on an agreed grant for each tank size.
• The partner appoints masons to build the tanks and ensures correct materials are delivered and quality is maintained.
• On completion, the partner sends the following to CED:
  • 3 photos:
    • one to show the gutters and inlet bucket,
    • one to show the tap and overflow,
    • one a general picture without people for sending to the donor.
  • Name of the recipient,
  • the village
  • GPS co-ordinates of the tank

CED invites individuals and churches to contribute to the programme. As a reward, people paying the full cost of a tank are sent a fridge magnet which helps publicise the programme. Tanks cost around £140 and CED sends 460,000 to the overseas partner so they can build a tank. This can be broken down into:

• Plinth for tank: £30
• The tank itself: £40
• Gutters/tap: £40
• Mould, supervision: £30
• Total cost: £140
• Gift Aided Donation: £112

We aim to deliver a fridge magnet within 21 days of you providing your address.

1. The tank is attractive; (in Kamembe, Rwanda someone asked if it was an art installation!).
2. The double curve distributes stresses more evenly. This is particularly important where the base meets the tank wall.
3. There is a generous factor of safety; double curve tanks of up to 4000 litres can be built without wire reinforcement (Watt, “Ferrocement Water Tanks”, 1978, p62).
4. The skeleton framework is easily manufactured locally and can be transported by bicycle.
5. Cement shell tanks are robust compared to plastic or steel tanks.
6. Cement shell tanks last much longer than plastic or steel tanks.
7. Cement shell tanks are easy to repair should a leak develop.
8. Cement shell tanks are heavy and difficult to move and therefore difficult to steal.
9. Cement shell tanks are economical to build.
   • Low cost of materials due to thin walls.
   • Whilst building tanks is a “specialist skill” it is easily learned.
   • Costs compare favourably against plastic tanks.
   • Building on site means that money stays in the community rather than being paid to city factories.

Our friends at SamSamWater have designed a tool which allows you to calculate storage requirements based on rainfall and roof area.

Rain from the sky is clean! Unfortunately, before it reaches the tank it runs down a roof on which birds have pooped and dust has gathered. For this reason books recommend the inclusion of a “first flush diverter” to catch the initial 10mm of a shower and divert it away from the tank. These, however, tend to be expensive and complicated. CED used a pipe with a stopper on the end but even this caused problems and was accepting very little water before it was full. We therefore rely on a mosquito wire sieve and a charcoal filter to offer some basic protection.

One study found that tank water is comparable in cleanliness to that fetched from protected rural point sources, averaging faecal coliform counts around 10 per 100ml which is just about WHO “low risk”.

If the tanks is kept sealed to prevent mosquitos and vermin and kept dark to reduce algae growth, the water actually becomes safer to drink with time.

We therefore ask for caution when drinking and encourage people to boil or use the “SODIS” decontamination method for water for their children.

In the long term we plan to start testing the water in a sample group of tanks.