There are various hard minerals in your tap water and the main culprits that produce hard water are magnesium and calcium. When these two come together, they form hard crystals which will stick to anything they come into contact with, and that’s why you get lime-scale.
SLOW PHOS technology works by altering the ionic charge of these troublesome minerals, which means they won’t be able to stick together and create lime-scale. This results in soft water that’s nice to drink as well as protecting your appliances. It also means that you still get the benefits of the minerals mentioned, which in small doses are good for you.