Does the sacrificial rod in a hot water heater - - the rod that very slowly disintegrates over the years - - add poisonous chemicals to the water in the tank and make the water unfit for drinking by humans?

Often called the stink rod because they smell pretty bad as they deteriorate, the rod does not create a danger to you. If they did nobody would be around to read this post. The water is the solvent in this case and it tries to dissolve anything it can. Rather than letting the water try to eat the heater lining a softer aluminium rod is offered and it dissolves easier and instead of the tank.