Regarding house plants, you will get them to root faster in plain tap water
and then transfer them to the pond/aquarium water. Seems nitrates actually
retard root starts.

My son & I found this out on a science experiment. We took root cuttings,
one was in tap water, the other in pond water. Was I ever surprised when it
was the tap water plant that took off. That's when I had to contact the
extension agent to find out why. ~ jan