I have few students that their final work at Biology was about growing Drosera capensis under different conditions. Few were grow with tap water compare to distilled water.the plants with tap water grown a bit smaller but the most important thing was that they had a salt secretion from the leaves you really can see the salts at the upper side of the leaves.
here are few photos so you can notice it
Arie
here are few photos so you can notice it
Arie