1. CONTEXT AND PROBLEM STATEMENT Access to drinking water in Peru has improved in recent years, yet significant disparities persist between urban and rural areas. By 2024, 98% of the urban population had access to basic drinking water services, compared to 87% in rural areas, reflecting since 2015 an increase of 3% and 13%, respectively. However, when considering safely managed drinking water—defined as services that are accessible, available, and free from contamination—coverage drops to 56% in urban areas and just 24% in rural areas. Relative to 2015, this represents a 3% decline in urban zones and a modest 4% gain in rural areas. Consequently, approximately 17 million Peruvians, half the country’s population, still lack access to safe water [1]. This vulnerability is especially pronounced in peri-urban areas of Lima. While residents in central Lima receive water from the public utility at an approximate cost of USD 0.8 per cubic meter, those in peri-urban zones pay between USD 5 and 7 per cubic meter—up to eight times more— for water of inferior quality and reliability. These households often have access to only 30 liters per person per day or less, compared to the virtually unlimited supply available in formal urban areas. Moreover, the water is frequently unsafe due to precarious transport and storage in unsuitable containers, and residents must wait between 0.5 and 1 hour daily to receive it. In rural areas, a critical challenge is the lack of knowledge regarding water quality. For instance, hydrogeological activity in the highlands of Tacna has been shown to contaminate the Sama and Locumba basins [2]. Similarly, some artesian wells in the Peruvian jungle contain polymetallic ions—such as arsenic and manganese—that exceed maximum permissible limits due to natural geogenic conditions [3,4]. In this context, there is an urgent need to develop water treatment technologies suited to rural and peri-urban communities, where access to economic resources, energy, chemical supplies, and skilled technical personnel is limited. Such technologies must be efficient, robust, easy to implement, and simple to maintain. Fortunately, Peru’s geographical location—extending up to 18°20' south—provides high-intensity solar radiation throughout the year [5], offering a valuable opportunity to leverage solar-based solutions adapted to the country’s complex terrain and limited transportation infrastructure. 2. METHODOLOGY 2.1 Experimental Setup and Reactor Configurations Three distinct types of solar photoreactors were developed and evaluated to test photocatalytic efficiency under different irradiation conditions and scales. 2.2. Non-Concentrating Flat-Plate Reactor A flexible, portable reactor was constructed using polyethylene (PE) sheets thermally fused at the edges to form a flat reaction chamber. Two configurations were tested with working volumes of 25 L (50x50x10 cm3) and 120 L. The system was equipped with inlet and outlet valves, a recirculation pump, and an integrated activated carbon filter to reduce suspended particles. A thin film of TiO2 photocatalyst was immobilized on the bottom inner surface of the reactor to maximize solar exposure. 2.2.1. PET Bottle Reactors (Low-Cost Disinfection) For simplified point-of-use experiments, standard polyethylene terephthalate (PET) bottles were utilized. These were modified to contain
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