Good water heaters are key. Mine is 200 liters and I've experienced cold water exactly once in three decades: One day 3 guests took hour-long showers each. Normally a family of five will never experience cold water.

The one I'm getting now has two coils, one to quickly heat water at the top half, the second to heat from the bottom - they're never on at the same time. Internal heat around 75 C, mixed to cooler on the way out, and it can keep hot water for 2 weeks if disconnected from power.