Certain policies have a once-and-for-all impact, while others
have a continuing or even a growing effect. Short-term measures introduced in
response to an emergency, such as a drought, may have a strong immediate impact,
but one which tails off sharply when the worst of the emergency is over.
Policies which make a long-term impression on water use, such as technological
adaptations and changes in user habits, are more sustainable.
Best of all are measures whose impact increases over time,
because their elements reinforce each other, or because they provide incentives
for continuing and cumulative