Should we pay more for an asparagus tin?

Some days ago I read this article in The Guardian which made me think why it is cheaper in many supermarkets to buy an asparagus tin from Peru than from my own country (I am from Spain and we have delicious and, many times expensive, asparagus).

http://www.guardian.co.uk/environment/2010/sep/15/peru-asparagus-british-wells

The key is, once more, the externalization of environmental costs, which in this particular case, are mainly referred to water management costs. As it is shown in the report, Peruvian asparagus are farmed in one of the driest places of the world. The immediate question here should be: who can start (and it seems that successfully) a farming business in this dry place? And even further, why and how is it possible? I am afraid these kind of intensive activities only can be affordable when the entrepreneur does not have to pay for the real value of the natural resources consumed. The resource in this case is water. Water must be a constitutional right in all countries; and population's access to water must be assured by law. If this statement were kept in mind by governments, then the taxes required to be paid by the farming companies should be proportional to the costs of the water management required in the concerned areas. This internalization of water security costs would be expected to impact and increase the production costs and subsequently the final price of products, here asparagus. Should we continue taking advantage of this unfair exploitation and buying "cheap" asparagus, or Peruvian asparagus at all? Of course, it is a complicate ethical dilemma, since these businesses also bring highly needed jobs to the inhabitants of these areas. Maybe the solution is just to ask for the sustainability of process in each of the products we consume; making the company to decide if the fair price derived from a fair (and sustainable) production system is still profitable and attractive to the consumers.