Hydrogen Detection

Trap the water vapor in a desiccant. You can use molecular sieves, aluminum oxide, silica jell, or any desiccant designed to trap water. Hydrogen is a much smaller molecule and will pass right through the desiccant. The desiccant will need to be dried when it becomes saturated, so size the drier for the gas flow you require.

What welderman said, except you might need to gauge the amount of moisture somehow prior to acquiring your dessicant system, in order to size this correctly. You may also experience some purity issues related to switching between dessicant vessels.

If you are searching for really helpful suggestions you should let us know what the carrier gas is (air??) as well as the required supply pressure, flow rate, and desired moisture level expressed as dew point, parts per million, or %RH. Desiccating driers are reliable and effective, but in some instances, a refrigeration drier might be preferred.