A sequence of isostructural lanthanide metal–organic frameworks (MOFs) [TbxEu1–xNa(HL2)2(H3L2)0.5]·EtOH [H3L2 = 5‐hydroxy‐isophthalic acid] (x = 0.1–0.9) are successfully obtained by doping TbIII and EuIII into the same framework. A fluent change in their photoluminescence is achieved by varying the ratio of TbIII/EuIII from 1:9 to 9:1. Among the obtained lanthanide MOFs, [Tb0.5Eu0.5Na(HL2)2(H3L2)0.5]·EtOH displays remarkable dual emission, with macroscopic bright red–orange luminescence in ethyl alcohol that is easily quenched, even with a low water content, thus presenting an innovative approach for an ideal chemical sensor for the detection of trace amounts of water in ethyl alcohol. As the water content increases, the probe exhibits a distinguishable change in its luminescence. To the best of our knowledge, it is quite rare for a self‐referencing luminescent sensor to be able to quantify the amount of water in ethyl alcohol over a wide range (0.01–3.2 %). The detection limit of the codoped Ln MOFs is 0.01 %, which is ahead of other reported MOF‐based sensors.