Using nano-TiO2 as a UV filter in sunscreens eventually leads to its release into the environment. Yet, understanding the behavior and fate of nano-TiO2, even in closed environments such as swimming pools, remains challenging due to the complex dynamics of environmental and nano-TiO2 interactions. This study characterizes (1) the behavior of nano-TiO2 in swimming pool water using single particle inductively coupled plasma mass spectrometry (ICP-MS) and (2) the efficacy of a commonly used cartridge pool filter in removing nano-TiO2 by acid-based digestion and quantification, as well as its accumulation on the filter using laser ablation (LA-)ICP-MS. The findings show that adding 40 g of sunscreen to the pool water significantly increases mass and particle number concentrations from about 300 ng TiO2/L and 5.8 × 104 particles/mL to 8605 ng TiO2/L and 2.0 × 106 particles/mL, respectively. However, almost 90% of the added nano-TiO2 was removed after 3 days of typical filtration cycles, and the average TiO2 particle size shifted from 92 nm after loading the pool with sunscreen to a size below 64 nm. Analysis of filter material confirmed the removal of Ti-containing particles by the filter, and LA-ICP-MS imaging revealed Ti accumulation close to the cartridge filter core, gradually spreading across the rest of the filter area.