Is the Amount of Water in the World Constant?

It’s roughly constant, like it’s constant but few things that change the amount of water, such as:

1. Sunlight split water vapor (the gaseus state of water) high in the atmosphere and the light hydrogen can escape to space.
2. We can gain water from space when comets or asteroids deliver some amounts of water, but this is minor.

What does change is usable water, not the whole amount of water in the world. The total amount of water is fixed, but accessible water can vary a lot. Only about 3% of water is fresh and most of that is frozen or in underground.

Water in the world is in closed system, it just cycles between oceans, atmosphere, ice, ground water, and living things, then evaporation, precipitation, runoff, etc.