In the highlands of southern Colombia and northern Ecuador, soils developed on volcanic ash deposits have specific properties: high water retention, high hydraulic conductivity and high carbon (C) contents. The main role of the soils is to regulate the water available for the dense population living in the valleys. Soil properties and land use depend on their altitudes. Any important modification of land-use change has a serious effect on soil properties and consequently the ecosystem properties such as water regulation and flood control. This can be a threat for a city that relies on the ecosystem for its water supply, as is the case in Ecuador's capital, Quito.