Is it safe to eat canned food past expiration date if the can were exposed to summer heat and freezing in the winter?
It isn't safe to eat canned food past the expiration date even though you expose to summer heat and freezing in the winter because the food has a special date.
Water is liquid and fluid. That means the water in that lake the next summer is new water and covers the lake bed that has been exposed to air and possibly freezing temperature during the preceding winter. I don't know how that would make the new water different from the water that had been drained.
Germany is mostly temperate. Extreme temperature lows and highs are rare. Winter temperatures vary from west to east, with around freezing temperatures in the west and well below freezing in the east of Germany. Summer temperatures are typically between 20°C and 30°C, with more rainfall during the summer months.