Article: Apart from residences for upper and middle class households, sanitation is insufficient in most residential areas. Private flush toilets are too expensive for virtually all residents in townships due to their water consumption and installation cost. As a result, access to improved sanitation has not increased much since independence: In Namibia's rural areas 13% of the population had more than basic sanitation, up from 8% in 1990. Many of Namibia's inhabitants have to resort to "flying toilets", plastic bags to defecate which after use are flung into the bush. The use of open areas close to residential land to urinate and defecate is very common and has been identified as a major health hazard.

Now answer this question: Most residential areas are insufficient in what area of Namibia?
sanitation