Editing Geography of Namibia (section)

===Water sources===
{{Main|Water supply and sanitation in Namibia}}
Namibia is the driest country in [[sub-Saharan Africa]] and depends largely on groundwater. With an average rainfall of about {{cvt|350|mm|in|0}} per annum, the highest rainfall occurs in the [[Caprivi Strip|Caprivi]] in the northeast (about {{cvt|600|mm|in|0}} per annum) and decreases in a westerly and southwesterly direction to as little as {{cvt|50|mm|in|0}} and less per annum at the coast. The only perennial rivers are found on the national borders with [[South Africa]], [[Angola]], [[Zambia]], and the short border with [[Botswana]] in the [[Caprivi Strip|Caprivi]]. In the interior of the country, surface water is available only in the summer months when rivers are in flood after exceptional rainfalls. Otherwise, surface water is restricted to a few large storage dams retaining and damming up these seasonal floods and their runoff. Where people do not live near perennial rivers or make use of storage dams, they are dependent on groundwater. Even isolated communities and those economic activities located far from good surface water sources, such as mining, agriculture, and tourism, can be supplied from groundwater over nearly 80% of the country.<ref>{{cite web |url=http://www.iwrm-namibia.info.na/iwrm/fundaments-in-iwrm/groundwater-in-namibia/index.php |title=Groundwater in Namibia |website=Integrated Water Resource Management |url-status=dead |archive-url=https://web.archive.org/web/20160729155617/http://www.iwrm-namibia.info.na/iwrm/fundaments-in-iwrm/groundwater-in-namibia/index.php |archive-date=29 July 2016 }}</ref> The longest river in Namibia is the [[Fish River (Namibia)|Fish River]] with a length of {{convert|650|km|mi|abbr=on}}.

More than 120,000 [[borehole]]s have been drilled in Namibia over the past century. One-third of these boreholes have been drilled dry.<ref>{{cite book |title=Groundwater in Namibia |url=http://www.namhydro.com/downloads.html |editor1=Greg Christelis |name-list-style=amp |editor2=Wilhelm Struckmeier |via=Namibian Hydrogeological Association |year=2001 |isbn=978-0-86976-571-5 |access-date=2018-07-10 |archive-url=https://web.archive.org/web/20150404091336/http://namhydro.com/downloads.html |archive-date=4 April 2015 |url-status=dead }}</ref> An [[aquifer]] called "Ohangwena II", located on both sides of the Angola-Namibia border, was discovered in 2012. This aquifer has been estimated to be capable of supplying the 800,000 people in the North for 400 years, at the current (2018) rate of consumption.<ref name=aqui>{{cite web|last=McGrath |first=Matt |url=https://www.bbc.co.uk/news/science-environment-18875385 |title=Vast aquifer found in Namibia could last for centuries |publisher=BBC World |date=20 July 2012 |access-date=10 September 2013}}</ref> Experts estimate that Namibia has {{convert|7720|km3|cumi|abbr=on}} of underground water.<ref name=afr>{{cite web|last=McGrath |first=Matt |url=https://www.bbc.co.uk/news/science-environment-17775211 |title='Huge' water resource exists under Africa |publisher=BBC World Service |date=20 April 2012 |access-date=10 September 2013}}</ref><ref name=aqmap>{{cite journal|vauthors=MacDonald AM, Bonsor HC, Dochartaigh BÉ, Taylor RG |doi=10.1088/1748-9326/7/2/024009|title=Quantitative maps of groundwater resources in Africa|journal=Environ. Res. Lett. |volume=7 |page=024009|year=2012|issue=2|bibcode=2012ERL.....7b4009M|citeseerx=10.1.1.693.4081|s2cid=154336728 }}</ref>

''Efundja'', the annual flooding of the northern parts of the country, often causes not only damage to infrastructure but loss of life.<ref>{{cite news
|url=http://www.unmultimedia.org/radio/english/2011/04/debilitating-floods-hit-northern-and-central-namibia/
|title=Debilitating floods hit northern and central Namibia
|last=Adams
|first=Gerry
|date=15 April 2011
|publisher=[[United Nations Radio]]
|access-date=23 April 2012
|archive-date=20 December 2016
|archive-url=https://web.archive.org/web/20161220185613/http://www.unmultimedia.org/radio/english/2011/04/debilitating-floods-hit-northern-and-central-namibia/
|url-status=dead
}}</ref> The rains that cause these floods originate in Angola, flow into Namibia's [[Cuvelai basin]], and fill the ''Oshanas'' ([[Oshiwambo]]: flood plains) there. The worst floods {{As of|2012|alt=so far}} occurred in March 2011 and displaced 21,000 people.<ref>{{cite news
|url=http://www.namibian.com.na/index.php?id=28&tx_ttnews%5Btt_news%5D=79689&no_cache=1
|title=Heaviest floods ever in Namibia
|last=van den Bosch
|first=Servaas
|date=29 March 2011
|work=[[The Namibian]]}}</ref>