Incorrect.
The Earth is constantly pelted with tons and tons of ice from space, and particles of dust , every day. There is actually more water on Earth than there used to be. And more Earth. The planet is growing in size, although not all of the growth is due to dust accumulation.
There is another side to that equation as well.
High in the atmosphere, water molecules are broken down into their constituent hydrogen and oxygen.
The hydrogen, which is lighter and faster, has more of a tendency to escape into space, leaving the monatomic oxygen atoms behind.