Reports about the housing situation in Kenya's capital, Nairobi, often focus on the lack of proper places to stay - particularly in the massive slum of Kibera, where tens of thousands live in appalling conditions. However, there are also areas of the city where too many residential properties are being built - or at least, being built too quickly. Development here is outstripping the provision of water, electricity and sewerage systems. And the result, greater numbers of people relying on limited infrastructure, is seen as a recipe for disaster.