Water demand management: is the glass 20% full or 80% empty?
In the face of excessive water development leading to economically marginal and environmentally detrimental supply-augmentation projects, water demand-management has been touted as an alternative policy answer. The term more broadly often encapsulates 1) measures aimed at reducing 'losses' in distribution systems and water use, 2) reducing 'demand' through various types of stick/carrots/sermon measures, 3) reallocating water to higher-value used, where the 'value' considered is more often than not monetary.
Water demand management has thus acquired wide currency in mainstream policy circles. By virtue of the negative images often associated with large infrastructure, demand management appears as a desirable and consensual softer and greener option that nobody is opposing. But what has demand-management really achieved in practice in the agricultural sector? What is its quantitative contribution to addressing the water crisis and avoiding further supply augmentation?
Several institutions or scientists consider that water demand principles provide 'a guide for moving from scarcity to sustainability' and entertain the idea that agriculture, in particular, can produce 'more with less' water, instilling optimism where actual overallocation of resources would warrant the opposite.
In a recent article Brian Richter and colleagues have undertaken, in their own words, "a comprehensive literature and internet survey" of water-saving strategies in irrigated agriculture, and have found that "that there is in fact considerable potential to reduce consumptive water use in irrigation systems". (They have also looked at cases of reallocation to other uses but since these transfers do not really save water I am not discussing such cases here). They have found 30 cases of water-saving measures, 10 of which being cases of "reduced water application". Cases of reduction in beneficial and/or non-beneficial consumption include cases of non-till farming, mulching, replacing open canals with pipes, irrigating at night rather than during the day, removing invasive and/or aquatic vegetation, and regulated deficit-irrigation. To which they add cases where shifting from a given crop to a less-demanding one would save water (they do not question why this is not happening in practice). Such inventories are much welcome and remind us of the various possible adjustments to scarcity, many of which are indeed implemented by the users themselves, when faced with water shortages.
I feel the belief in whether such measures and practices can make a difference, and whether their potential is indeed 'considerable', so as to put us on the track of sustainability is very much a question of seeing the glass '20% full' or '80% empty', as there is now way to even estimate the quantitative potential of cumulated measures. Evidence from studies on closed/overexploited basins and aquifers certainly puts me, however reluctantly, on the side of those who see the glass 80% empty (at best).
Two fundamental facts, I believe, are not properly considered: first, in situations of over-commitment and unsustainable use of resources, the only solution is reducing consumption. Thus demand-management measures almost invariably come at a cost (more labour, more capital, less water, etc) and are therefore not popular with neither end-users nor managers and politicians. Irrigation water pricing has proved totally ineffective for reasons that are now well understood and that include the political impossibility to charge water at the high level necessary to curb use. Attempts at organizing users or basin/aquifer stakeholders have very seldom been successful, when users realize what they stand to lose.
Second, since such measures reducing the benefit of water are unpopular and/or costly, it is understandingly only well after water scarcity has built up and become structural that these measures are tentatively imposed. This means that the basin is already largely closed and the aquifer dropping at alarming rates. Return flows (even polluted) have long been tapped and (re)used wherever possible, thanks to increasingly cheap pumping devices. This hydrological reality, also recognized by Richter and colleagues, means that the gains that can be expected from measures that reduce the volume of water applied are often minimal.
Most water demand-management policies are mistakenly geared towards reducing the amount of water apply and not its consumption, and in fact frequently increase the latter (the promotion of drip in conjunction with vegetable and fruit tree is an ubiquitous example: see a recent review and a case study). As allocation tends to a zero sum game the benefit drawn from consuming water can be spatially reallocated but water scarcity and overdraft can increasingly only be dealt with through a reduction in evapotranspiration. This is what happens sooner or later: farmers are pumped out and get out of the agricultural sector, groundwater-dependent vegetation dies, and wetland dry up. Demand-management can do little at this stage and the supply-demand gap ends up materializing in a dramatic way.