Here’s some studies about the bactericidal and disinfecting effects of sunlight:
Note: This is an extensive scholarly article covering the antimicrobial and wound-healing effects of ultraviolet radiation, including as a treatment for antibiotic-resistant pathogens.
Note: Article covering the disinfectant/germicidal effects of ultraviolet light.4
Conclusion: This 11-month study of a wastewater system found that solar UV light is an important element in the natural purification of water.
Conclusion: This 1877 study placed four test tubes of solution on a window sill exposed to sunlight, with four other test tubes of solution being entirely shielded from light. After twelve days, the solution in the unexposed test tubes had become “milky” from bacteria proliferation while the solution in the test tubes receiving sun exposure was still clear and clean in appearance. The solution of the exposed test tubes continued to appear clean and clear even after a full month, but no data exists after this due to the test tubes being accidentally disposed of. This article also goes on to explain that this experiment had been repeated many times with the same result. The only exception is that the apparent bactericidal effects of sun exposure appeared to be reduced on cloudy days. The researchers also found that sun exposure retarded the proliferation bacteria even when the test tubes were deliberately infected. Is regular sun exposure important for our personal hygiene? Are sun-loving nudists more free of bacteria compared to sun-avoiding vampires?