[Technetium]

When you dissolve sodium hydroxide granules in cold tap water, a pungent gas is given off. Is there some component in domestic tap water that reacts to produce a gas. It could be chlorine (from the water purification process). The tap water is medium hard so contains a certain amount of dissolved salts but not calcium.Any advice as I have been unable to find anything online about this reaction.

[Arkcon]

We had a similar question recently:  http://www.chemicalforums.com/index.php?topic=83381.0

[Technetium]

This refers to hydrogen or water vapour being given off due to the heat involved in the dissolving process. The gas I experienced was pungent to my nose (not hydrogen or water!).

[Borek]

The gas I experienced was pungent to my nose

And this is addressed in the thread linked to by Arckon - the fumes are not just pure water, but most likely a caustic aerosol.

Put a litmus paper into the fumes and see how it behaves.