Some of the most important things to understand about water use, in this time when concerned over world water shortages is being expressed, are that:
• together we are only using about 10% of the total renewable resource, or 'available' supply (approx. 40,000 out of 400,00 km3);
• a huge fraction of this is not beneficially used, it is just wasted because it is not perceived as sufficiently costly to be worth conserving;
• even in the highest water using countries (which are usually affluent, hot and dry, so that large quantities are required for irrigation) the fraction of the available supply which has been developed so far is only in the 40-50% range, and;
• on the lowest water using continent, Africa, the fraction of the available fresh water used is down in the 3-5 % range. The critical constraint here is, typically, inadequate financing for water development, rather than any absolute water shortage.