Is there anything water cannot dissolve?

What Can’t Water Dissolve?

Water is often called the "universal solvent" because it dissolves more substances than any other liquid. But despite its impressive abilities, there are clear limits to what water can actually dissolve.

Water excels at breaking apart ionic compounds—like table salt—because its molecules are polar, meaning they carry a slight electrical charge. This allows water to pull ions apart and surround them. However, non-ionic substances don’t respond to water’s polarity. For example, oil and other non-ionic organic molecules don’t mix with water. That’s why salad dressing separates and why grease doesn’t simply wash away with water alone.

Similarly, most metals and elemental substances—like gold, iron, or carbon in the form of graphite—don’t dissolve in water under normal conditions. While water can contribute to the corrosion or oxidation of metals over time (think rust on iron), that’s a chemical reaction, not true dissolution.

It's also important to distinguish dissolving from physically breaking down. Water can erode rocks over centuries through freeze-thaw cycles or mechanical action, but that doesn’t mean the rock dissolves. The minerals remain intact, just fragmented. True dissolution means the substance’s molecules disperse at the molecular level—something water can't achieve with non-polar or highly stable materials.

So while water is remarkably versatile, it’s not all-powerful. Its ability to dissolve depends heavily on the chemical nature of the substance it encounters. When polarity doesn’t match, even the most persistent water can’t make a difference.