>...I had been
> infected by Giardia Lambia, excuse the spelling. It was a parasite that is
> too small for the cleaning system that was cleansing the river Neva from
> which the city took its water.

The city was filtering its water properly (ex. via sand or membrane
filtration).  Disinfection usually isn't adequate to inactivate giardia and
cryptosporidium (which is smaller than giardia).

Rob