What UK Homeowners Should Know About Hard vs. Soft Water in Pools

If you own a swimming pool in the UK, you’ll know that water quality management is essential. One factor that is overlooked is whether the water in your area is naturally hard or soft. This difference, caused by the mineral content of your mains supply, can significantly affect pool maintenance, equipment lifespan and swimmer comfort. 

What Does “Hard” and “Soft” Water Mean?

Hard water, contains higher levels of dissolved minerals, mainly calcium and magnesium. Soft water, has very low mineral content, often less than 100 parts per million (ppm) of calcium hardness. 

In the UK, water hardness varies widely depending on location. For example:

• South East England, based around us in Beaconsfield. London, Kent, Essex, Oxfordshire, etc, is predominantly hard water. 

• Scotland, North West England, Cornwall, Wales, etc, are mostly soft water areas. 

To ensure what your area is, you can check your water supplier’s website for a hardness rating specific to your postcode.

Why Water Hardness Matters for Pools

Water hardness plays a vital role in keeping swimming pools safe and long-lasting. In areas with hard water, which is common for most of southern England, excess calcium can cause limescale to form on tiles, liners and equipment. Over time, this buildup can clog filters, reduce the efficiency of heating and pumps and even make the water appear cloudy as minerals fall out of solution. 

Pools filled with soft water face different issues. Low calcium levels make water more aggressive, which can lead to corrosion of metal fixtures like ladders and heat exchangers, as well as damage to tiled or concrete surfaces. Swimmers could also notice that soft water feels harsher on the skin and eyes. Due to this, UK pool treat guidelines recommend maintaining calcium hardness between 200-400 ppm to keep the right balance and avoid scaling and corrosion. 

How to Adjust Pool Water Hardness

If your pool is located in a hard water areas the main challenge is controlling excess calcium. Too much hardness leads to scale forming on surfaces and equipment, so it’s important ti use a scale inhibitor to help prevent deposits from building up. Regular testing is essential, as high pH levels increase the risk of scaling, and keeping both hardness and pH in balance will protect your pool’s efficiency. 

For homeowners in soft water regions, the issue is the opposite. Water without enough minerals becomes aggressive and can damage pool fittings and surfaces. In these cases, a calcium hardness increaser, like calcium chloride, should be added to bring levels into the recommended 200-400 ppm range. It is also best to avoid topping up with rainwater, which is naturally low in minerals and can make the problems worse. To keep everything in check, calcium hardness should be tested at least once a month during the swimming season, with a full water balance check by a professional carried out annually. 

Looking for More Advice?

Whether you live in a hard water area or a soft water region, managing calcium hardness is a crucial part of swimming pool care. You must be able to keep levels within the recommended range to protect the pool equipment, prevent scaling and corrosion and ensure a safe and comfortable swimming experience for the family. 

Get in touch with Deep End Pools for more information or a water balance check.