First of all, let’s address the issue of Hard Water. What does that mean? Hardness is a measure of the amount of Calcium & Magnesium salt that is present in water.
Rainwater is naturally soft because it has no mineral content. As it seeps through the ground it can potentially pick up minerals, such as calcium and magnesium. Very small particles of calcium and magnesium(ions) dissolve into water as it passes through or over soft rocks like limestone or chalk.
Map of water hardness levels for the uk
Hardness is made up of two parts: temporary (carbonate) and permanent (non-carbonate) hardness. When water is boiled, a portion of the hardness, the temporary hardness, forms a calcium carbonate scale, which can deposit on kettle elements as limescale. The permanent hardness does not do this when water boils and stays dissolved in the water.
If you live in the Forest of Dean or Wye Valley then you probably get your water from Severn Trent or Welsh Water. You can check your water quality & hardness by going to either website.
What are the signs of Hard Water?
There are no regulatory limits for water hardness. Several studies have shown that hard water provides some benefit to health, although the exact mechanism is unclear. For example, some studies have shown evidence of less heart disease in areas with a hard water supply.
The problems of scaling in kettles, water heaters, cylinders, combi boilers etc is caused by the calcium carbonate scale or limescale. This can build up at a rate of around 1.5mm per year, as the build up gets greater the efficiency of the appliance rapidly decreases leading to eventual failure. British Water claim that a 1.6mm build up of scale in a heating system will result in a 12% loss in heat transfer from the energy source to water.
The average life of a boiler heat exchanger is 10-15 years. In hard water areas, this can be cut by nearly 80%, reducing the life expectancy to just 2-3 years.
The UK Building Regulations Part L covers the conservation of fuel and power and has been recently updated to place a greater emphasis on improving the energy efficiency of homes.
This is as a result of upcoming carbon emissions targets set by the Government, and hard water areas have been identified as an area in particular where efficiency levels could be improved.
Written to assist installers, the UK Building Regulations Compliance Guide suggests how best installers of heating and hot water systems might comply with the Regulations with regards to hard water. It recommends that:
‘Where the mains water hardness exceeds 200 parts per million, and if required by the manufacturer, provision should be made to treat the feed water to water heaters and the hot water circuit of combination boilers to reduce the rate of accumulation of limescale.’
Scale Inhibitors interfere with the formation of calcium carbonate, they do NOT soften water. The calcium & magnesium is still present in the water but the molecular structure is altered so that limescale doesn’t “stick” to surfaces and can be more easily wiped off. For more information on Water Softeners see other post.
Types of Scale Inhibitor
Electrolytic works by passing the water through a tube containing a Zinc anode which alters the structure of the limescale crystals so that they don’t stick to each other or to surfaces. The limescale now can be wiped off surfaces with a cloth.
Magnetic works by passing the water through a tube surrounded by a magnet. The magnetic field again alters the crystalline structure of the limescale so it does not stick to itself or surfaces.
Electronic works by passing the water through an electrical field, usually via 2 wires wrapped around a section of pipe, connected to a controller which generates high frequency square waves in a random waveform which again disrupts the limescale crystals.
Chemical or Polyphosphate dosing works by introducing a measured amount of food grade polyphosphates to the water which forms a protective film on surfaces so the limescale crystals don’t stick. The polyphosphate cartridges have to be replaced 6 monthly or annually, depending on usage.
All the different types of scale inhibitor work to varying degrees, the electronic requires a power supply and consumes around £5 per year of electricity. Electrolytic inhibitors last around 10 years, the polyphosphate cartridges for combi boilers have to be replaced every 12 months. The Sentinel CombiGuard/ AquaDial refill which is fitted to the cold supply of a combi boiler is around £52 per year = £1 per week.