I'm looking for ways to help mitigate California's drought. I've come up with two ideas. The first is a pipeline from Washington. The pipeline could be built with similar construction principles to an oil pipeline, which is a pretty mature process. The water could be sold to California municipalities for a tidy profit. But the time and cost of building such a pipeline would be prohibitive. My second idea is a passive offshore desalination rig. This is what I want to focus on right now. Desalination seems to be a pretty popular topic, here. The design would be a large geodesic dome made entirely of glass. Lensed glass, such as fresnel lenses, to focus more light towards the center of the dome. The center of the dome would consist of a basin which fills with sea water with the tide. The basin would need to be insulated (so it doesn't boil the surrounding seawater) and the filling mechanism would need to be filtered (so fish etc. don't get caught in it). The inside rim of the dome would have a catch basin above high tide sea level. This would lead to pipes and a pumping system to pump the water to land. I'm picturing them being somewhere between 40 and 100 feet in diameter, but that depends on a lot of math. In simple terms, the dome focuses the sunlight to heat and evaporate the water while acting as a heat sink to reclaim the steam and condense it for use. Potential hurdles: - Cost. Building an offshore rig, materials for building the rig, manpower to manage filling and cleaning the basins. - Energy. Energy cost to pump the water to shore and to its final destinations. - Location. Would need a lot of room on a continental shelf. Would also need a beachside pumping station to receive and distribute the distilled water. - Efficiency. How much water can a single platform distil? How big will the rig have to be? Can the process be adjusted to be more efficient? Can it be modified to generate electricity? How many rigs would be needed to make a difference to California's water needs? - Comparability. How does the cost and efficiency compare to pumping coastal groundwater? Possible solutions: - Cost. Concrete and composite lenses are fairly inexpensive compared to other materials. Existing oil rig designs could be modified to suit the design. - Energy. I need math. It's possible that the rig could produce electricity by heating the water into steam and running it through a turbine. The excess steam is then reclaimed as distilled water. Based on my limited understanding of existing solar thermal power plants, each rig would have to be fairly large to capture enough solar power to make this effective. The idea is that these could be built relatively cheaply, that they could be operated with minimal cost, minimal moving parts, minimal maintenance. That they may not be able to produce as much water as an active desalination plant through boiling or osmosis, but the cost difference would make up for it. That dozens or hundreds of these could be built offshore along California's coastline and begin providing fresh water within the next couple of months. That the low cost and simple construction could make them available fairly quickly. Where I run into trouble is efficiency and math. I suspect someone's already done the math on ideas similar to this and just couldn't get them to distill enough water to be cost effective. I'd like some help to determine how inefficient this would be - it's possible that we can make them more efficient - like an array of mirrors such as those found at a typical solar thermal plant.