"Mike Lyle" wrote
snip
Question: does water-pepper taste good enough to be used in food?

I can't find anything actually recommending it to eat, although there are
lots of references to it having a hot peppery taste when chewed. This
webpage says it has 'an acrid biting juice':
http://more-than-mint.kategilby.co.u...rs/wldfl10.txt which
doesn't sound very palatable. I can't see it listed in Richard Mabey's food
for free.

It apparently used to used to repel fleas in bedlinen and had folk names
such as Smartweed and Arsmart because it caused a smarting sensation to
skin - presumably when it was left in the bed by mistake.