Here is a good question I was asked pertaining to the adding of additional water (not blessed), to a holy water font at home containing Holy Water - Does the water added gain the blessing of the Holy water that it is added to?
In Christ Jesus...^i^
Answer by Rev. Mark J. Gantley, JCL on 10/2/2007:
I don't know of any directive that encourages merely adding new water to holy water to make more holy water.
To me this seems silly. Just get a container and a priest or deacon bless some more water. It takes a few seconds.