Natural replenishment of this vast supply of underground water occurs very slowly.

靠自然补充大量地下水是十分缓慢的。

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In some countries the supply of water from underground can be the only source of water available.

在一些国家由地下水供给的水是仅有的可用水源。

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So, water enterprises need a set of effective and convenient methods to manage the water supply network which is valuable underground resource in cities.

为此，企业需要一种方便、高效的方式来管理城市宝贵的地下资源——自来水管网。

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However, this year the Namibian department of water affairs announced the discovery of a significant body of underground water - an aquifer dubbed Ohangwena II - that scientists say could supply the north of the country with enough water for centuries.

CNN: Namibia country profile: moving on from a difficult past

But Mr Cheney said it was underground water that mattered most for long-term supply.

BBC: Jersey water boss wants water behaviour change

Other solutions are more complex, but still cheap, such as injecting a sugary mixture into a water supply contaminated by hexavalent chromium to make it less toxic and less mobile underground.

FORBES: The World's Most Polluted Places