The interlinking of the hydrogen and hydrological cycles implies that availability of water, for either electrolysis or other means of splitting it into its constituent elements, is a crucial factor in achieving sustainable, renewable and "clean" production routes for gaseous hydrogen.
The Earth is 70 % covered by water, but 97 % of this is saline, leaving around 2.5 % as directly electrolysable freshwater. Ofthe freshwater budget, only 1 % is available for direct use, as the balance is frozen in the global ice caps. Current IPCC assessments  note that many areas of the world are likely to experience water stress. It is estimated that up to 2.3 Bn people worldwide live in areas where the annual availability of water is less than 1700 m3/year. To compound the problem, 30 % of
freshwater sources are aquifer-based. Such sources have long replenishment cycles and may not be renewable in practical timescales.
For the developed countries the emergence of extra water demand for hydrogen production is unlikely to be critical. The projected annual demand for hydrogen generated by migrating the US light transportation fleet to hydrogen fuel  is estimated as 150 Mtonnes/year, which is equivalent to 100 billion gallons of water/year. As domestic water usage in the US is around 4800 billion gallons/year and conventional power generation is 70 trillion, the amount needed for hydrogen generation would not be a significant perturbation. As noted above, for developing countries with existing water stress constraints, diversion of water to the production of hydrogen could be more problematic. The advent of new technologies may present a unique opportunity for third World countries to break the existing cycle of energy related indebtedness. Whilst poor in petrochemical resources many third World countries are rich in solar and other sustainable energy sources. Appropriate combinations of aid and technology support could thus alleviate poverty and energy dependence.
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