This is the VOA Special English Development Report.

Safe drinking water has always been rare and valuable. Throughout the world, drinking water has to be stored for periods of low rainfall. Tanks or other containers for water storage must be ready long before a dry season begins.

For hundreds of years different kinds of materials have been used to build water storage containers. In many areas of the world, small lakes or reservoirs formed by dirt walls provide drinking water for villagers during the long dry season. In western Sudan, the thick part of the baobob tree is removed to store water collected during the short rainy season in that country.

Bricks and concrete are among the modern materials used today to build storage containers for water. A solid rock can be used as the bottom of a water tank. However, a mixture of rock and soil should not be used. The soil will settle down, but the rock will not. The water will leak out.

Ferro-cement structures are popular in some developing countries, especially in India. Ferro-cement is made by pouring a sand and cement mixture over a skeleton form made of steel rods, pipe, or chicken wire. It creates a structure that is lightweight yet keeps in water. The walls of ferro-cement structures are usually thin, which means that they can be used in building different shapes such as circles.

Wood also can be used for water storage structures. Cypress, fir, pine and redwood are some of the kinds of trees that have been used. Wooden tanks do not require special care, although their average lifetime is shorter than tanks made with concrete or steel. Any chemicals used to keep the wood from being ruined must not be poisonous substances.

Water in uncovered storage tanks or reservoirs can become unsafe. Small green plants called algae can grow in large amounts near the surface. The algae may help bacteria continue to grow, even if chemicals such as chlorine are added to the water to kill the bacteria. Uncovered water also can be polluted by birds, animals or humans.

You can learn more about storing water for drinking through the Volunteers in Technical Assistance, or VITA. VITA is on the Internet at www.vita.org.

This VOA Special English Development Report was written by Gary Garriott.