Global population is projected to increase over year 2000 levels by 30% in 2025 and by 50% in 2050. Producing sufficient food to feed a more populous Earth will be a challenge requiring additional developed water supplies. Existing supplies are unevenly distributed around the planet. Some developing countries lack sufficient water to grow the food necessary to feed the growing population. With time, more countries will join that group. The strategies available to produce more food depend upon which sources are available. Two options open to all countries are improving the productivity of water in agriculture and importing virtual water in food. For some, the additional options of bringing more land into production or harvesting rainwater may also be available. All these measures reallocate water to agricultural uses from environmental uses. Such reallocations may impose potentially large losses in the form of environmental services and environmental amenities. Difficult water allocation decisions with enormous values at stake confront humanity. These decisions are confounded because they entail the protection of the global commons for which there is no successful experience to draw on.

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