There are a few examples of rainwater harvesting at http://practicalaction.org/irrigation-answers. Have a look at the document infiltration pits which Practical Action has been involved in in Zimbabwe.

However, it’s probably less applicable in the Turkana region because of the rain patterns. The Turkana region is part of the rift valley and in Kenya the Turkana region is fed by rivers; these are mainly the Omo River from the Ethiopian highland and the Turkwell and the Kerio rivers from the south of Kenya. The rivers feed into Lake Turkana. These water sources replenish the groundwater in the region.

The amount of water in the region as a whole can vary considerable due to erratic rains. These are commonly seasonal but also vary from year to year with many years having very little rain. This results in the water table dropping along with the level of Lake Turkana. The rivers tend to be dry for parts of the year. This situation has been made more complicated with the addition of large-scale dams such as the Gilgel Gibe III dam on the river Omo and the Turkwell Gorge Dam.

Generally the population is quite sparse in the region with large regions used by pastoralists with others smaller areas used by farmers but the population has grown in some regions and competition for grazing land does produce conflicts, especially in times of drought.