One of the main needs of the modern society is the availability of low-cost energy sources, and the solar energy arises as an interesting alternative for both the generation of heat and electricity. In this work, a low-cost solar energy reservoir is proposed for domestic water heating. It is comprised of a thermoplastic (polyethylene) water tank thermally insulated by means of two different polymeric coatings, an acrylonitrile butadiene rubber foam, NBR, and a metalized polyester layer. The solar system also contains a flat collector based on a ceiling panel made of poly(vinyl chloride), PVC, coated with carbon black-filled glaze. The system design is cost-effective because of all the parts involved in the solar heating are made from commodity plastic materials. These plastic components present wide commercial availability and are easily handled, so that they can be rapidly assembled to build the entire system. Therefore, the solar heating system is simple, modular and easy-scalable, and may be even self-manufactured by the final user. It is an affordable option to the traditional high-cost copper, aluminum and glass solar panels and boilers or tanks used for heat storage.