I'm puzzled by this,help~~~

Hello sprint.

Do you swim?

If someone swims, but not very well - they are just able to keep their head above water.

The saying refers to situations, often financial, where people are having difficulty, but are just barely able to manage.

For example, someone who is working and paying their bills, but has no extra money at all, could be said to be keeping their head above water (in an economic/financial sense).

Thank you!