Acid-based reverse osmosis scale inhibitor is a broad-spectrum anti-scaling agent suitable for all water sources, particularly groundwater. It is especially effective against scaling caused by metal oxides, silica, as well as carbonate, sulfate, and iron oxide deposits. It exhibits high scale inhibition efficiency and does not coagulate with residual coagulants or silicon compounds rich in aluminum and iron to form insoluble polymers. In reverse osmosis (RO), nanofiltration (NF), or ultrafiltration (UF) systems without ion exchange pretreatment, it prevents scaling, increases water production, and improves product water quality.