annealing is the process of softening a metal. To anneal copper, you heat it until it glows and then cool it either slowly or quickly.
To anneal steel, you use the same process, but it must not be cooled quickly or it will re-harden.
Copper cannot he hardened uniformly in the field. Copper pipe is rolled in the factory to make it hard. Once you anneal it, theres no going back.
What you may have experienced was hydrogen embrittlement in which hydrogen from the water damaged the hot copper. This is more prominent with low grade copper.