It depends on the Whisky, and the person, but you can dilute to taste. With a stronger whisky you will be able to experience and enjoy a wider range of flavour if you dilute it a little. Some whisky will be able to take as much as a third again of water, some only a few drops... and some nothing at all.

Don't worry!

If you add too much water you can always add some more whisky. (hic).