Non-use” values refer to water that people will not actually use themselves at any point, but may want to preserve for others, for future generations, or simply because they attach a value to their very existence. It is particularly difficult in situations when irreversibility and possible disastrous outcomes enter the equation, and when the resilience of water systems is being - or is close to being - overrun. This is not an argument against trying to make as good an assessment as one can, but it makes it particularly important to take into account those cost and benefit elements that cannot be expressed in monetary terms.