Here we numerically demonstrate that photolytic processes induced by external ultraviolet (UV) sources considerably affect the chemical properties of plasma-water systems. When describing the chemical transport between surface dielectric barrier discharge (SDBD) and deionized water, the plasma is simulated using a global model, while the gas (air) and liquid (water) regions are considered in a one-dimensional space. Our simulation involving exposure of plasma-treated water (PTW) to UV shows that long-lived species in PTW are readily photolyzed and form hydroxyl radical (OH) and nitric oxide (NO) over the entire liquid region. The total OH concentration was enhanced by 11.6 times at 100 s under exposure to a conventional UV lamp, while the total NO concentration was remarkably enhanced up to 45.8 times at 300 s. The time at which the OH concentration notably increases was advanced by more than 100 s by photolytic processes. The results directly reveal that the exposure of PTW to UV is an attractive approach to selectively releasing extra OH and NO, thereby increasing the PTW reactivity and applicability. Owing to their high reactivity and oxidizing power, the short lifetime of radicals including OH and NO in PTW, which is crucial in diverse applications, has been troublesome. In this regard, our findings will provide new guidance in utilizing PTW for various applications.