P. Ball,
«Solutions for reducing borehole costs in rural Africa». Water and Sanitation Program - African Region, Nairobi, Kenya, p. 12 p. : 6 fig., photogr., 1 tab., 2004.
P. Ball,
«Solutions vers la reduction du cout des puits d'eau en milieu rural Africain». Water and Sanitation Program - African Region, Nairobi, Kenya, p. 16 p. : 6 fig., photogr., 1 tab., 2004.