Small communities far from the municipal seat do not have access to drinking water, so many children suffer from various gastrointestinal diseases, which cause these children to grow up with nutritional deficiencies. In the state of Campeche, there are 300 sunny days. This energy can be used to install water treatment systems to make it drinkable. Therefore, a treatment system with heterogeneous photocatalysis was proposed using a zinc oxide catalyst doped with silver nanoparticles. The reactor has a metal structure with a flat plate where clay plates support the catalyst. Samples were taken every 2 h to carry out the corresponding analyses and in a period of 8 h of reaction. For the characterization of rainwater adhered to Mexican regulations. The results showed that there was 6400 NMP/100 mL for fecal coliforms at the beginning, and after 4 h, this parameter goes to <2 NMP/100 mL. Initially, the same happened for fecal coliforms; 9200 NMP/100 mL was determined. After 4 h, this parameter drops to <2 NMP/100 mL. The same behavior was observed with chlorides, hardness, and total alkalinity, which showed a tendency to decrease significantly. This confirms that the system works properly to eliminate organic compounds and purify rainwater.