How hard is my water?
If you call your water authority they will probably give you some scientific answer. The response will be in parts per million, or ppm. How many ppm will make my water hard? There are different degrees of hardness. According to the US Geological Survey, (http://waterdata.usgs.gov/nwis/qw) 88.3% of homes in the US have what is considered hard water. Hard water begins at about 100 ppm. For most homes this does not cause major problems but can slowly build up in appliances use and heat water. Anything over 180ppm is considered extremely hard.
How does it affect your machine?
Minerals will line your machine, especially in the boiler. They make crusty deposits which, over time, can create blockages. It can also adversely affect the heating element of your machine causing inefficient heating. As well as break the heating element if you have an internal heating element that is directly exposed to the water. The scale is like ice and can get into every part of your coffee maker or espresso machine and break it apart. Especially the tiny o'rings and seals that are soft. This can cause leaking in your machine which can lead to its total failure. Repairs that are caused by scale buildup are usually very costly and almost always are not covered by your warranty.
How to prevent build up - regular maintenance!
It is critical that you descale or decalcify (these terms are interchangeable in the espresso world) on a regular basis. Even if you do not have very hard water, you should still descale on a regular basis to clean out the coffee brewing components of your machine. Coffee can also build up in your machine and cause clogs. You can also use water with a lower mineral content. Some machines (Expobar, Pasquini, Rocket Espresso, HX or heat exchange machine, etc) need at least some minerals in their water for their auto-fill feature to operate properly. Consult your manual or call tech support if you are not sure if your machine requires some minerals in the water. Most machines do not require any sort of special water. But by avoiding water with high ppm counts, you will extend the life of your machine and keep your coffee tasting great.
How do descalers work?
Descalers are acids and release Hydrogen ions when dissolved in water. The H+ ions eat away at the scale by using the charge (+) to pull at the deposited minerals. A mild acid based descaler should be sufficient to get your machine cleaned safely and effectively. Make sure to follow the directions in your manual for your specific machine as well as the directions on the descaling product itself.