There's really no reason to wash a phone under running water, unless it's horrifically filthy. Although the phone is IP68, remember that it's
not a guarantee that the phone will be unaffected by water exposure. It's water
resistant, not water
proof. Look at page 5 of the manual:
http://downloadcenter.samsung.com/co...1.0_160219.pdf
"
Despite this classification, it is still possible for your device to be damaged in certain situations." It's very vaguely worded, but it's essentially a disclaimer that means the warranty won't cover any potential water damage.
Just use a microfiber cloth to clean the screen and body, and if there are stains, use a little bit of rubbing alcohol.