The impact of the environment on the electrical properties of uncapped In0.5Ga0.5As nanostructures is studied as a function of different atmospheres for sensing applications. Electrical response from surface quantum dots (QD) shows a strong dependence on the atmosphere, in contrast to the response of 2D nanostructures. The sheet resistance drops by 99% from vacuum to air, and decreases more than one order of magnitude when relative humidity changes from 0 to 70%. The adsorption of water molecules onto the QD surface improves the conductivity likely by reducing the density of surface states acting as carrier traps, which enhances electron transport.