Hard Water is called that because it contains mineral build-ups such as magnesium and calcium ions. This makes soap less effective on them. Hard water leaves traces, so it will be easy to identify if you have hard water or not by observing the surface of your bathrooms.  Hard water marks look like scales, and you can find them on plumbing, sink tops, and faucets.  Some ways can assure you whether or not you have hard water. The most common tests are as follows. Take a clear bottle and fill it up with a significant amount of water, like 300-350 ml. Add 10 to 12 drops of liquid soap into the bottle of water. Soap reacts to hard water more, so this will give you an estimate of how much hard water your tap water has. Shake the bottle well. When you open it, look for soapy bubbles on the top. If your water is very soapy, that means the hard water concentration is more, and vice versa. To check further, add more soap. The hard water level will depend on how many drops of soap you need to add to make the soap suds appear. If you end up using 30-40 drops to make the soap suds appear, then your water is hard. For best results, use liquid hand soap for this experiment.