Many of the world's irrigation areas, however, from wealthy to less developed nations, are highly stressed and drawing more water than rivers and groundwater reserves can sustain.
Freshwater food reserves are also declining in the face of the quickening pace of dam construction and unsustainable water extractions from rivers.
'Millions of people depend on freshwater fisheries as a major food source,' Mr Leape said. 'Freshwater food stocks can provide up to 80 per cent of dietary protein for the 60 million people of the Mekong basin, for example. And that's just one river.'
WWF is taking a major role in World Water Week to highlight a host of other water related problems and their potential solutions.
Faltering river systems are increasing conflict, reducing power production, weakening important aquatic transport networks and increasing health risks - not least through reduced performance in transporting and naturally treating wastes.
Wetlands in particular play a major role in reducing disaster impacts and in climate regulation, with peatlands covering just 3-4 per cent of world land area but containing an estimated 25-30 per cent of the carbon in terrestrial vegetation and soils. Release of this stored carbon would be enough to raise global temperatures by 2-3º C.
'Freshwater systems are home to around 40 per cent of all the species on earth,' Mr Leape said. 'And our impact is shown by the fact that we are losing these species faster than any other.'
Mr Leape said the world was a long way from being ready for a worsening water crisis, with profligate water use still the rule rather than the exception, protection and management schemes for only a minority of freshwater reserves and effective protection and management for only a minority of schemes.
'A global treaty for co-operatively managing rivers and lakes that cross or form borders is still languishing in limbo more than a decade after being approved by a clear majority in the United Nations,' Mr Leape said.
WWF will spend the week in Stockholm outlining solutions to the water crisis grounded in its work with governments, business and communities world wide.
'Water management for human needs alone is damaging the natural systems we all depend on,' Mr Leape said. 'No management is even worse.
'Maintaining the health of freshwater ecosystems has to become one of the major aims of freshwater management generally.'
WWF is to present studies showing the water footprint of the UK and conference hosts Sweden extends to some of the driest and most under-privileged areas of the world - but both water exporting and water importing areas can do much to reduce their demand on water resources.
'We are also concerned that the world continues to mainly discuss adaption to climate change rather than doing it,' Mr Leape said. 'We have been doing it, all over the world, and we have found that that improving the health of freshwater ecosystems now makes a great contribution to improving their resilience to climate impacts in the future.
'It is ironic that currently it is not foresight and planning but major natural disasters that lead to significant efforts to repair damaged rivers and wetlands. Foresight and planning now will reduce the risk and damage from future extreme weather events, while having many economic, social and environmental benefits.'
Of the world's total water resources, 97.5 per cent is salty and of the remaining but mainly frozen freshwater, only one per cent is available for human use.
'Even this tiny proportion, however, would be enough for humans to live on earth if the water cycle was properly functioning and if we managed our water use wisely,' Mr Leape said.