Replenishing holy water

[Dominicus]

I heard that if a priest or font were not available it was possible to replenish holy water by adding a lesser amount of regular water, is this true? If so can it be done multiple times if necessary?

On a similar note, does adding blessed salt to regular water make holy water, or does sprinkling holy water on an object in a way bless it? Obviously not the same as having a priest bless it directly but it has to count for something right?

Just curious but answers are appreciated.