Sheet erosion is the uniform removement of soil. Rill erosion is a linear form of soil erosion by water and occurs when flowing water accumulations. Gully erosion occurs when the flowing water creates channels wider than 40 cm. The gully heads develop uphill.

Read more in the section about the 'Resource soil'.

In the case of demand exceeding availability the term ‘physical scarcity’ is used, whereas ‘economical scarcity’ means that a resource is available in a sufficient quantity, but access is limited.

The major advantage of PIT latrines is that faeces can be used to produce useful biomass. The main disadvantage is that they are often polluting groundwater if they are not placed carefully.

More inforamtion on the impact of PIT latrines on the groundwater will be provide in the section about the 'resource water', more information about the use of faeces as biomass in the section about the 'resource biomass'.