How much silica gel are you working with? If the amount is small enough, you may be able to put it on a rotary evaporator. Put the silica in the flask and start it rotating. Put a light vacuum on the system. Use the suction "straw" that one can use to add more solvent/sample into the flask. Add the water a little at a time. The rotation causes the silica to be mixed will. This allows you to control the amount of water added.

Another way to add the water is to make the 2:8 EtOAc/Hexane and partition it with water- the solvent will become saturated with water. Pack the column in this solvent, and flush (equilibrate) with about 5 to 10 column volumes of the saturated solvent. The column will adsorb whatever water it can and reach equilibrium with the solvent.

If you keep your silica gel in steam vapours for 1-2 hours it will change color from dark blue to light pink. The exact quantity of Water can be used in normal portable home steam vaporiser. Time may vary depends on amount of water vapours. The inactivated silica gel is light pink colored.

 Dear

What kind of chromatography you are up to. However is the water is part of assay.

Assuming you want to prepare 100g of 12% water deactivated silica gel (please note: 12% of the total weight!), add 12g of water, drop by drop while agitating, to 88g silica gel (activate  at 120-250°C x 16h). Agitate by hand or mechanically (the longer the better!): the powder must be free flowing and no lumps should be present. Allow 12h to equilibrate (under agitation, if possible) before use.

Thank you very much for all your suggestions. It's very helpful. I need to do separation of a mixture of methylene blue and sample product by using deactivated silica gel (12%v/w water) in chromatography.