Question

how is that materials that are much denser than water

Answer 1

I am guessing by materials you means something like solid compounds compared to liquid water.

First of all ALMOST all chemicals, solutions, substances that go from gas to liquid to solid become more dense as less kinetic energy exists between its components. If there is less kinetic energy, there is less movement of particles and they are more or less fixed in position (unlike gases and liquids that fill the container). Water is a good exception to this due to its hydrogen bonds.

If you need any further clarification, just let me know!