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Malawi is generally considered to be relatively rich in water resources, which are stored in the form of lakes, rivers and aquifers.
The country is divided into 17 Water Resources Areas (WRAs), which are subdivided into 78 Water Resources Units (WRUs). There are two major drainage systems:
- The Lake Malawi system, which is part of the Zambezi River basin. The Shire River is the only outlet of the lake with an average flow of 400 m3/s. About 91 percent of the country is located in the Zambezi River basin.
- The Lake Chilwa system, which is shared with Mozambique. Lake Chilwa is an endorheic basin draining rivers originating from the eastern slopes of the Shire Highlands, the Zomba Plateau and the northern slopes of the Mulanje Massif.
There are two main aquifers in Malawi:
- The Precambrian weathered basement complex, which is extensive but low yielding (up to 2 l/s);
- The quaternary alluvial aquifers of the lakeshore plains and the Lower Shire valley, which are high yielding (up to 20 l/s).
Malawi’s total renewable water resources are estimated at 17.28 km3/yr (Table 2). From this, 16.14 km3/yr are produced internally, while about 1 km3/yr comes from Mozambique via the Ruo River and 0.14 km3/yr is from a lake shared with Mozambique along the course of the Shire River. Almost all of the internal groundwater resources of 1.4 km3/yr are thought to be drained by the rivers, as Malawi is a humid, enclosed country. Water resource distribution is highly variable both seasonally and geographically, as nearly 90 percent of the runoff in major rivers occurs between December and June.
Lakes are a main feature of Malawi’s water resources and the main ones are:
- Lake Malawi, which is the third largest freshwater lake in Africa and the eleventh largest in the world, has a total surface area of 28 760 km2 (including the part of the lake belonging to Mozambique). The lake is 570 km long, 16 to 80 km wide, and has a total storage of 1 000 km3. Its average depth is 426 m, while its maximum depth is 700 m. It is the most important single water resource and plays a vital role in the socio-economic development of the country.
- Lake Malombe covers 303 km2, is about 30 km long, 15 km wide and has an average depth of 4 m.
- Lake Chilwa lies on the border between Malawi and Mozambique. Being the "sink" of an endorheic basin, its surface area is very variable but is on average 683 km2, of which 721 km2 lies in Malawi. It is a shallow, saline lake with an average depth of 2 m.
- Lake Chiuta, separated from Lake Chilwa by a sand bar of 20-25 m height, lies on the border between Malawi and Mozambique. It covers 200 km2 of which 40 km2 belong to Mozambique. Its depth is 5 m.
There are nine major dams with a height of more than 12 m and with a total storage of slightly over 43 million m3. They have been constructed mainly for municipal water supply, except for two that were constructed in the 1950s near Blantyre for hydroelectric purposes. In addition there are 700 750 small dams with a storage capacity of approximately 64 million m3, most of which were built during the colonial period and are in various states of disrepair. Due to lack of maintenance over a long period, most of these small dams require major rehabilitation. Currently the government has embarked on the rehabilitation of some of these small dams through various programmes as part of the national water conservation strategy. According to the Water Resources Board, any dam with a dam height of 4.5 m and above is classified as a large dam; for that reason, dam design reports and drawings have to be available for technical consideration when a water right application is processed.
Malawi is rich in wetlands, which include lakes, rivers, many reservoirs spread over the country and marshes. The most important marshes are the Elephant and Ndindi marshes in the Lower Shire Valley, the Vwaza Marsh in the Rumphi district, and the Chia Lagoon in Nkhotakota. The major wetlands of Lake Malawi and Lake Chilwa are closely monitored under the RAMSAR and UN biodiversity conventions.
The history of groundwater development in Malawi dates back as far as the early 1930s. By 1994, there were about 9 600 boreholes and 5 600 protected shallow wells, the majority of which were constructed by the government. However, since then the increase in boreholes drilled by the government, non-governmental organizations and the private sector has been dramatic, and according to the Ministry of Water Development there were about 19 000 boreholes drilled in 2001. This trend is continuing and the number of boreholes is continually increasing as a result of the proliferation of drilling contractors in the country. Furthermore, due to the recent frequent occurrence of droughts, the number of hand-dug shallow wells has considerably decreased because they are highly vulnerable and prone to drying up, and therefore people have opted for boreholes instead of shallow wells.