What makes something food?
You don't get energy from breaking chemical bonds, you only get energy from making chemical bonds, while breaking chemical bonds requires the input of energy.  However, in practice chemical bonds are always broken as others are formed, and the net number of bonds is generally constant.  Otherwise you would end up with free radicals, which are highly reactive and looking to form a chemical bond with the next thing it touches.

For example, the burning of glucose in respiration involves the breaking of C-C, C-H, C-O and O-H bonds in glucose and O=O bonds in oxygen, with the simultaneous formation of C=O bonds in CO2 and O-H bonds in water.  But the C=O bonds in CO2 and O-H bonds in water contain much less energy than the bonds we break within in glucose.  So the key is that the bonds formed contain less energy than the bonds broken, and energy is released overall.

And actually it's a bit more complicated than that, because you also have to consider entropy, which is how disordered the system is.  Generally the more molecules in a system, the more entropy, so breaking a few big molecules down into lots of small molecules tends to release energy by increasing entropy.

So to answer your question, "food" is what we can draw useful energy from in the process of turning it into something else as we make and break chemical bonds.  We can't do this with water, or indeed with rocks, because their chemical bonds would require more energy to break than the energy we'd get back out by forming alternative bonds with anything else.