In multi-purpose water systems, power asymmetry is often responsible of inefficient and inequitable water allocations. Climate Change and anthropogenic pressure are expected to exacerbate such disparities at the expense of already disadvantaged groups. The intervention of a third party, charged with redefining water sharing policies to give greater consideration to equity and social justice, may be desirable. Nevertheless, to be accepted by private actors, this interposition should be coupled with some form of compensation. For a public agency, compensation measures may be burdensome, especially when the allowance is triggered by natural events whose timing and magnitude are subject to uncertainty. In this context, index based insurance con...