" Paula Berkebile" wrote:

There's friction from the water molecules rubbing against each other as they
flow. Friction raises the temperature of the water. Got this from my
resident chemist.

I am a physicist and physics is the study of energy, not chemistry.
Actually physical chemistry studies phase changes like the freezing of
water. However, I will undauntedly state that the energy of friction
provides a very negligible amount of heating. It is usually negated by
the cooling that occurs when compressed liquids are decompressed. To
see exactly how negligible this energy is, the same flow could be
generated by gravity and the pools at the bottom of water falls don't
get warm. In fact some of the biggest water falls and biggest rivers
have been known to freeze solid.

The reason that moving water usually doesn't freeze is that there is
usually some source of heat, the ground, the pump or something else, and
the circulation spreads the heat around so that it is less likely for
the water to freeze.

In your home the outside spigots don't freeze if you let the water
trickle through because the water in the house is too warm to freeze
when it flows out.

Actually too energetic a pump can make things worse by robbing all the
heat out of the ground under the pond. It is optimum to have a pump just
big enough to keep the water circulated so some of the heat from the
bottom makes it to the top and keeps a hole open.

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