Read the following passage and answer the question that follows. Your answer should be based on the passage only.

Many cities have pledged to eliminate water shortages within the next two decades, which would require domestic water waste to fall close to zero. A hydrologist reckons that, at best, only a third of this saving might be achieved through demand-side measures, such as households fixing leaking taps and taking shorter showers. And even that would require utilities and municipal bodies to offer stronger incentives, through pricing and rebates, to make water-efficient fixtures cheaper and more widely available.

Which one of the following statements best reflects the central idea conveyed by the passage?