Chloramine is pretty nasty stuff, and people should perhaps take care when using it in their water tanks. It's quite toxic (to humans and fish), and doesn't degrade naturally like chlorine. And it can't be removed by boiling the water. So it would be necessary to flush the tank with fresh water very thoroughly. It's reckoned that about 10% of the UK's water is now treated with chloramine, but obviously in very tiny concentrations.