Hello Peter,
A minor point, the Carver Crystal is a water filter and the Cascade is the water heater. As both the Carver and Truma heaters do not "Boil" the water they should only be referred to as heaters.
As with any domestic hot water system it is unwise to use water that has been stored at an elevated temperature. Both the Truma and Carver water heaters retain an air cap above the water, and this is a potential site for bacteria and the deadly legionalla.
If the systems did boil the water then the dangers would be much reduced, but as they only heated to a maximum of 72C and more typically only 55 to 60, then it is possible that the water could become unfit to drink or ingest.
It is also another reason why regular cleaning of your water systems with an appropriate agent should be carried out to reduce the risk of contamination.