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Back to water tanks. Say, you need a 2 m² ferrocement water tank for your [http://www.akvo.org/blog/?p=813 rainwater harvesting system]. The classical technique is to start with building a [http://vimeo.com/8367598 cage of steel reinforcement bars], covered with chicken wire mesh. An alternative is to start with an [http://vimeo.com/channels/emas#8453558 inner form of metal sheets], which is later removed. Or, for smaller tanks, a sack filled with sand is used. Once this structure is established, a cement mixture is applied. As ferrocement is much stronger than masonry, the thickness of the walls is in the range of 10-30mm. During curing (at least 10 days, although 30 is better) the cement is kept wet and wrapped in plastic sheet. Fill’r up, and enjoy.

Your tank will be a lot cheaper than a plastic tank, have a lifetime of at least 25 years, and is easy to repair in case of cracks. The technology is extremely simple to implement, and semi-skilled construction workers can learn it with ease. Such tanks have been used on a wide scale in Asia and in some African countries, and there is huge scope for increased use for rainwater harvesting systems.