Current water-heating technologies in developing countries are either expensive or have poor quality that increase health and environmental risks. CalSolAgua (CSA) designed a simple, yet patentable, low cost solar water heating system capable of reducing energy costs and carbon emissions for households in developing countries. CSA’s solar water heater can sell for onethird of the price of competing water tank heaters and less than one-eighth the cost of existing solar water heaters. Additionally, it will reduce carbon emissions by over 90 million tons, which is equivalent to taking 17 million cars off the roads. As a 2008 Big Ideas award recipient, CSA has made considerable progress in developing its technology, partnerships and business model. The team will build off this foundation by launching sales in Guatemala and preparing to launch in Mexico City through market research and test installations, to be followed by expansion to Brazil, China and India.