A national system of interconnected water pipelines joining all 50 States should be constructed.
Climate change will bring significant problems to many States, such as higher incidences of extreme/unusual weather. This means everything from drought to flooding, incidents which can have lasting negative impacts on our environments and livelihoods. The US needs a way of alleviating drought in certain States, while on the other hand controlling flooding in other States. This proposal could make dealing with these issues easier, if not solve them.
Furthermore, when water supplies are damaged by human activity (ex: spills from oil drilling), the pipelines could be used to provide clean water to those affected and possibly dilute contaminated water supplies enough to make them safe again.