Place the butter in a saucepan on medium heat. Slowly let the butter melt.
After the butter is melt and still warm, remove the whitish casein that floats on the surface carefully with a spoon, and discard it.
After you have removed all the casein pour the liquid butter in a bowl. Do not pour completely all the liquid. The water has separated from the butter and still sits in the bottom.
Pour the rest of the liquid in a clear glass. You will see the water in the bottom of the glass, and you will be able to easily recover all the butter and discard the water.