how big is the barrel???
first thing to know about barrels is keep them moist, letting them dry then re swelling can cause problems.. CAN not WILL.... mold, and distorted planks are two of the big issues. keep the water in it until your ready to use it. the big issue your gonna have is sanitizing it.
this is how i sanitize for wine making
To sanitize your barrel, fill it half full of water. Dissolve the proper amount of sodium bisulphite in a little water and pour it in the barrel. Then dissolve the proper amount of citric acid in a little water and pour it into the barrel. Now bung up the barrel and mix well by shaking or rolling the barrel. Finish filling the barrel with water and bung tightly. Check the water in the barrel from time to time, completely filling it each time.
When you're ready to use the barrel, rinse it out, then fill it again with fresh water and leave it overnight. Rinse out the barrel again, and it is ready to use.
Use one-half pound of citric acid and one pound (0.45 kg) of sodium bisulphite for each 50 gallons (190 L) of barrel capacity. Do not use less than the stated amounts.