Abstract: Water in a gas is measured with improved sensitivity to low levels (on the order of 2.000 to 0.005 ppmv), response time and cell longevity, by an electrolytic cell wherein the electrode element comprises a tubular conduit for the gas having a pair of electrode wires helically positioned in parallel on the interior wall of the conduit from end to end, the wires being coated, except for small portions adjacent the inlet and outlet of the conduit, with a water absorbent crystalline coating comprising a mixture of phosphoric acid or a derivative thereof and an alkylene (C.sub.2 -C.sub.4) oxide polymer selected from a polyalkylene glycol of average molecular weight of at least 500 and an ether or ester thereof having an average molecular weight of at least 300.