If your concern is storage you want as hot as possible, less boiling. Thermostatic mixing valves can bring the temp down to a safe temperature for use.
Losses are higher but you store more energy per L, which is often the limiting factor.
Losses are higher but you store more energy per L, which is often the limiting factor.
I think that what actually costs money is not the space but the tank. Higher temperatures mean not only more expensive materials and shorter lifetimes for tanks and piping but also higher conductive losses.
1. Consider PCM heat storage (still relatively new technology, but works well with heat pumps)
2. Maybe the problem shall be solved at the building level, not individual apartments.