There are actually two opportunities for leakage in the area you specified.
The first would be where the water supply line attaches to the plastic piece that is sandwhiching the porcelan tank. The other would be the plastic piece that sandwhiches the tank and accept the supply line. Turn the water supply off, disconnect the supply line and tighten the plastic piece that is remaining on the tank. Reattach your supply line, turn the water back on and you should be all set assuming there are no cracked fittings, stripped threads, rotted gaskets or corrosion. A little silicon grease on the fittings wouldn't hurt either.