What's a safe way to clean the touch-mouse thing on a laptop?

I use a handkerchief dampened with distilled water on the LCD screen. The moisture is wiped off with a dry part of the handkercheif before the screen dries on its own. I think it would be OK to give a touchpad the same treatment.

I use distilled water because I live in a hard water area and find tap water can leave smears, probably because a slight deposit of limescale gets left behind.

Some recommend mixing isopropyl alcohol with water but I've never found that necessary.