No but it tastes way better, I usually clean whatever piece I am using at the beginning of the day. Might even clean them 2-3 times depending on how many people are using it. I can't stand hitting a bong with day old water. Try hitting a piece that hasn't been cleaned in a while, tastes like shit, I don't want my weed tasting like shit.
Lately the taste of dirty bong water leaves me feeling sick, so personally fresh water gets me higher because I don't feel like shit lol.
Yes fresh water is rich in nutrients such as thc. That's why I don't smoke weed anymore and just drink water.