Bacteriophages targeting Pseudomonas spp. were isolated and characterised for the biocontrol pre- treatment of rainwater. Bacteriophages PAW33 and PFW25 were characterised as members of the Podoviridae and Myoviridae families, respectively. Bacteriophage PAW33 displayed specific activity against Pseudomonas aeruginosa (P. aeruginosa) strains and was applied in small-scale bacteriophage pre- treatment trials (8 h and 24 h) to restrict the proliferation of an environmental P. aeruginosa S1 68 strain. Hereafter, the respective samples (bacteriophage pre-treated and non-pre-treated samples) were subjected to treatment in small-scale SODIS compound parabolic collector (SODIS-CPC) systems for 4 h under natural sunlight. For the 8 h pre-treatment and SODIS-CPC trials, similar total log reductions in colony forming units (CFU) per mL and gene copies (GC) per mL were obtained for the bacteriophage pre- treated [3.68log (CFU) and 2.34log (GC)] and non-pre-treated [3.74log (CFU) and 2.33log (GC)] samples. In contrast, for the 24 h trial (followed by SODIS) a higher CFU per mL log reduction was recorded for the pre-treated sample (4.61log) in comparison to the non-pre-treated sample (3.91log), with comparable results obtained using EMA-qPCR. Gene expression analysis indicated that PAW33 pre-treatment for 24 h influenced the ability of P. aeruginosa S1 68 to initiate stress response mechanisms (decreased expression of the recA and lexA genes) during the SODIS-CPC treatment and resulted in the decreased expression of the phzM gene (virulence factor responsible for pyocyanin production). Bacteriophage PAW33 thus displays promise as a pre-treatment strategy of rainwater as it restricts the proliferation of P. aeruginosa and may increase the efficiency of primary disinfection methods.