It is recommended that you do not drink or cook with the hot water from the tap. Domestic hot water never gets hot enough to kill anything in the water. However it does stay warm enough to be a wonderful breeding ground for stuff you should not be drinking. It is suspected that Legionaires disease is one of the more common health risk that may result. Many topics out on the web on this subject. I know many people are out there doing it everyday and not seeing any problems but for me and my family it is not worth the risk.
http://www.niehs.nih.gov/external/faq/legion.htm http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_g.htm
Another good reason to flush the tank regularly.
