typically megaloc is used for gas connections. i haven't seen it used for water although i don't personally know of any reason it can't be used for water. for other pipe joints i prefer real tuff to pro dope. real tuff has teflon particles mixed in the compound which lubricate the joint as you tighten making it a little easier to get the joint a little tighter and also the particles help pack the joint threads the way thread wick does when used with the older joint compounds (like pro dope).
