Often in the world there is a shortage of water, this situation can lead to war.

Collecting large amounts of rain water for later use is not only a life line in the event of drought but strategically important too.

  In many places in the world water just
runs off mountains and hills, it
erodes the ground and in many places makes
deep ravines; the minerals and soil are then
washed out to sea.

For third world countries and places where very
low cost is imperative both the erosion and
collection can be improved by local small scale
reservoir systems.

 
Existing streams that only fill in the wet season could be partly diverted into a reservoir. The reservoir is lined with sheets of recycled rubber (made from car tyres). To prevent evaporation a simple straw flat roof is put in place over the reservoir. 

Other roof designs could also be adopted. For example, there is even possibility of growing crops on the roof of the reservoir by placing a thin layer of soil on top of the roof. I envisage a box system with each box filled with approximately 6cm of soil.  The roof does not need to support the farmers weight as he can stand in the reservoir and move the boxes around on the supporting post.

The reservoir is slowly emptied in the dry season
using known irrigation techniques.

This is an excellent way of reusing old car tyres

There are millions of old tyres going to land fill each year.
If the rubber can be melted then separated from the metal banding and made into rubber sheets perhaps 5mm thick. This process must be simple and be
achieved in communities around the world.

Low cost is imperative so here are some variants

Clay lined instead of rubber storage tank.