Water is regarded as a "universal solvent". The reason behind this is the property of the water. Water is a solvent that can dissolve a variety of substances in itself. Any other liquid cannot dissolve the number of substances that the solvent water can. The reason behind being the universal solvent is the chemical composition and physical characteristics of water.
Once you have identified the limiting reactant, you calculate how much of the other reactant it must have reacted with and subtract from the original amount.
