Rain Water Storage Tanks
Once collected, the rainwater needs to be stored for later use. Below are a few examples of low-tech construction techniques.
Pumpkin Tank from Sri Lanka
This version uses hessian rather than ferro-cement
‘Thai Jar’ being built as part of a Water and Sanitation Programme in Tanzania
Here a ferro-cement tank is constructed on the outside of a galvanised iron form
This in-ground tank is built from bricks and mortar, which is then mortared to seal it.
Figure 1 – detail drawing of the
A simple, conventional in-ground tank
Simple dug cistern lined with mortar. Note the inlet siste, which filters silt from surface collected water.
Some interesting historical aspects -
According to an Archaeological Encyclopedia,
The first cisterns were dug in the Middle and Late Bronze Age [2200-1200 B.C.; LW]. The rainwater that collected in them during the short rainy season would be enough for at least one dry season. In some parts of Palestine cisterns were the main (sometimes even the only) source of drinking water in peace time as well as in war time. In the early Iron Age [1200-1000 B.C.; LW] the sides of cisterns began to be covered with watertight plaster, which considerably prolonged the time for which water could be stored. It was this important innovation that made it possible to extend the areas of settlement into the mountainous parts of the country. 
In Petra [...] huge cisterns were hewn in the rocks into which the rain water was run through surface channels. These cisterns were high up in the side of the rock, so as to prevent defilement. The interior was divided by rock partitions into reservoirs, oft-times many in number, and so arranged that when one was full it would overflow into another. In these rock-hewn reservoirs millions of gallons of water could be stored and be always cool, clean, and available.