Vegetables lose nutrients when cooked in soup. Water brought to a boil transfers heat quickly to vegetables, which causes some of the nutrients inside them to seep out into the cooking water. However, the nutrients resistant to heat will stay in the soup — and you will eat them along with the water.
Heat degrades some of the vitamins contained in vegetables, such as vitamin C, folate, and pantothenic acid, and strengthens others, like lycopene in tomatoes.
https://homecookworld.com/vegetable-nutrients-in-soup/