Regular cleaning of your espresso machine is a key step to being able to continue to pull the perfect espresso shot just like you did when your machine was new. All tap water, and even most bottle water, contains minerals, and over time calcium forms a hard deposit in the plumbing of your machine. Unless you remove these deposits on a regular basis, your machine will become less able to pump the water and maintain the correct pressure necessary for making espresso. The calcium deposits, which are the same ones you may have observed on the insides of a kettle, are gray and very hard. The chemical composition of the calcium is alkaline and is removed by exposing it to an acid solution. Most of the descalers you buy off the shelf have citric acid in them. Another "home remedy" is to use a vinegar solution. I recommend and use an inexpensive cleaner called Cleancaf which is available from Amazon.com. Just like your teeth, regular cleaning of your espresso machine avoids bigger problems down the track.