Warm salted water for swolen feet

I used to play basketball when I was a kid and it was frequent for me to go home with strained ankle which would cause a swolen foot. My mum would always prepare a bowl with salted warm water for me to immerse my foot on for a while.

The swelling would go down but, to be quite honest, I cannot say if it was because of the warm water, because of the salt, or because it would go down without any treatment anyway.

I have also heard her suggest the same to a couple of people when she noticed them with swolen feet and legs due to pregnancy.