Water is known as the "universal solvent" because -
It dissolves more substances than any other liquid or most of the substances can be dissolved in water.
Water molecules have a polar arrangement of oxygen and hydrogen atoms that allows the water molecule to become attracted to many other different types of molecules.
The positive part of other ionic molecules is attracted to the oxygen side of the water and the negative part of the compound is attracted to the hydrogen side of the water.
It can dissolve most of the ionic and polar covalent compounds like salts, acids, and bases.
Therefore, water is known as the universal solvent.