Abstract: A method of filtering feed liquid including a photoresist substance comprises removing cations from the feed liquid using an ion exchange material. A fine particle filter filters the feed liquid and, in particular, removes dissolved solids from the feed liquid. The material is regenerated with a solution, e.g., a brine solution, which has a pH effective to avoid fouling of at least one of the filter and the ion exchange material. Another embodiment concerns a filtration apparatus including an ion exchange device containing the ion exchange material. A fine particle filtration device removes dissolved solids from the liquid. A device for regenerating the material includes a supply of the regenerating solution.