If you need a best in class water softening and filtration solution that is easy to install and maintain, Londinium Espresso are now selling one; http://londiniumespresso.com/products/everpure-claris-water-filter-and-softener
We are the first to acknowledge that proper water softening (using hydrogen ion replacement, not the cheap but now illegal sodium ion replacement) is a significant running cost.
The problem is that if you have a water supply high in calcium carbonate the cost of not adequately protecting your investment in your espresso machine is far greater.
Not only will your machine fail; the limescale will actually clog the inlet to the boiler to the extent that it will no longer fill fast enough to replace the water you are drawing off, but the process of descaling a machine is very very hard on all aspects of the machine. Heavily scaled machines often have the limescale chipped out of them with a cold chisel, before being placed in a bath of sulphuric acid for a week or more to eat away the calcium carbonate deposits. This process is very hard on all the joins, welds, seems, threads, seals, and fittings, despite as many of these being removed as possible prior to embarking on the process.
Unsurprisingly once a machine has been subject to this process a couple of times nothing quite works in the manner in which it left the factory.
If you bite the bullet and put a strong water filtration and softening system in place you will extend the life of your espresso machine by decades. Furthermore it will hold tolerance and be much easier to set and adjust and the espresso that you produce from your machine will be significantly better.
Limescale in an area like London will kill the finest and most elaborate espresso machine that money can buy in less than 12 months. In fact the more complex and sophisticated your machine the more sensitive it is to limescale deposits. It doesnt just accumulate in the boiler, but it clogs valves and gauges. Every single component in contact with the hot water is at risk