Well he was not clear. Some of you use pre-chillers to cool tank water and an immersion chiller. All the self made counter flow chillers used on wort here in the USA use copper for the inside that has wort flowing through it, and cheep clear plastic tubing (same as used for transfer tubing) as the outside. Who cares what the hot water tastes like, I do care what the final beer will taste like. Copper is a good conductor of heat.
Do not have the specs for a home built counter flow chiller, however I would think about 3 meters of copper would work. The fun part of home builts is finding the correct fittings for the ends. You dont want cold or warm water all over the place.
Home built counter flow chillers are not as efficient as a real one. If your water is not cold enough then you will not get very good results. Our tap water is cold and you get pitchable wort with as fast of a flow as you can get with a commercial chiller. Good results from home made ones if they are long enough, though you may have to slow the wort down a bit.
So if you are using Copper for the inside, then use whatever you have that fits the fittings you have for the ends for the outside. If you are going to drink or water the garden then I would use something suitable.
See how easy it would have been for them to answer my simple question? I could have given a simple answer instead of a long one with out all the stupid posts to clog up the thread.
