Membrane-Based Water for Injection Systems segmentation by type distinguishes three primary membrane technologies: reverse osmosis (RO), nanofiltration (NF) and ultrafiltration (UF). RO membranes, characterized by pore sizes below 0.1 nm, achieve the highest salt rejection and are the dominant driver of market revenue, accounting for roughly 55 % of total system sales because they satisfy the most stringent USP <659> purity specifications for injectable drug manufacturing. NF membranes, with pore diameters between 0.5 and 2 nm, provide a balance between solute rejection and permeate flux, supporting formulations that require selective removal of divalent ions; they contribute approximately 30 % of the market value, particularly in biopharmaceutical intermediates. UF membranes, featuring larger pores (0.01–0.1 µm), are employed where microbial and particulate removal suffices, representing the remaining 15 % of sales, mainly in hospital pharmacy compounding units. Collectively, these sub‑types shape the overall market size by allocating capital expenditure according to required purity levels, operational cost, and equipment footprint.