Abstract: Using seawater as a benchmark of water with high TDS (total dissolved solids) Raw seawater can be instantly and significantly desalted just by passing a flow through adsorber (FTA) without applying electricity to the adsorbent therein. Various precursors may be converted to dual-functional adsorbents for the FTA. A cation-adsorbing group and an anion-adsorbing group are grafted onto the surface of the adsorbents by phosphorylation and amination, respectively. Based on the applications, the adsorbent may be configured as membrane form or packed bed in the FTA. When the adsorbent becomes saturated, it can be regenerated online using liquids cleaner than the intake. Besides seawater, the FTA may be utilized for treating other TDS-infested wastewaters at very minimal cost.