Hard water rarely causes a sudden failure. Instead, it gradually coats heating elements, narrows pipework and increases the energy needed to heat water. For a café, salon, small clinic or serviced office, the signs may include longer heat-up times, more frequent service calls and equipment wearing out earlier than expected.
The Drinking Water Inspectorate (DWI) explains that hardness is not a safety problem, but the resulting scale can shorten appliance life and reduce efficiency. Here is how to check your water hardness, protect different types of equipment and plan routine maintenance.
Key takeaways
- Know your water hardness. The DWI classifies water containing 200 to 300 mg/L of calcium carbonate as hard and water above 300 mg/L as very hard.
- Treat scale as an efficiency issue. Even a thin layer can make water-heating equipment work harder.
- Start with settings and maintenance. Correct hardness settings, salt dosing and descaling intervals can prevent avoidable problems.
- Treat water where it matters. The DWI notes that softening the supply before a hot water tank or boiler may be more economical than treating the whole building.
- Keep a written record. Log test results, servicing, descaling and changes to appliance settings.
Where hard water occurs in the UK
Water hardness is usually measured in milligrams per litre of calcium carbonate. The DWI classifies 200 to 300 mg/L as hard and anything above 300 mg/L as very hard. It also cites World Health Organization guidance that water at or above 200 mg/L is likely to produce scale, while water at or below 100 mg/L can be more corrosive to pipework. Both ends of the range can therefore affect maintenance.
Local geology drives the pattern. Thames Water, for example, says most water in the South East is naturally hard. Conditions can still vary by location, so use your water supplier’s postcode checker or water quality report rather than relying on a regional map.
Why a thin layer of scale costs money
When hard water is heated, dissolved calcium and magnesium can form deposits on hot surfaces such as elements, heat exchangers and boiler walls. Scale conducts heat poorly, so the burner or element must run longer to transfer the same amount of heat into the water.
Published figures should be treated as general guidance rather than predictions for a particular appliance. Energy Institute training material has estimated that 1 mm of limescale on a boiler’s water-side heat exchanger can add roughly 5% to 7% to the energy required to meet the same heat demand. A CIBSE Journal CPD example also indicated an efficiency loss of about 7% from a 1 mm layer on a water-heater tank. These older examples show the likely scale of the issue, but actual losses depend on the equipment and operating conditions.
How hard water affects different equipment
The symptoms and maintenance requirements depend on where water is heated, stored or sprayed. Always follow the equipment manual because acceptable hardness levels and descaling methods vary.
Heating and hot water systems
Common warning signs include kettling noises, longer recovery times and uneven heating. Heating and Hotwater Industry Council guidance published in 2025, aligned with BS 7593:2019+A1:2024, recommends protective measures where incoming hardness exceeds 200 ppm. It also calls for annual water testing and appropriate documentation. Warranty terms may require evidence that suitable protection and maintenance were in place.
A practical annual routine is to check incoming hardness, test the system water, replenish inhibitor where required and clean filters or strainers. Complete any flushing or cleaning specified in the service schedule. Do not reduce stored hot water temperatures simply to limit scaling. Temperature settings may form part of legionella controls, so follow the manufacturer, your risk assessment and professional advice.
Commercial kitchen equipment
Dishwashers, combi ovens and countertop water boilers can accumulate scale quickly. Bosch dishwasher instructions, for example, tell users to identify local hardness and enter the matching machine setting so salt dosing can be adjusted. Siemens notes that some combination detergents are effective only up to a stated hardness, above which separate salt and rinse aid are required.
Commercial water-boiler manuals, including those from Instanta, commonly require regular descaling in hard-water areas. Some manufacturers also specify a scale reducer or water softener and may link warranty coverage to suitable water treatment. Check these requirements when equipment is installed rather than after a fault occurs.
Laundry equipment and small appliances
Washing machines, kettles and hand-wash boilers are also vulnerable to scale. Descale them at the interval stated in the manual, and periodically inspect inlet filters, spray outlets and tap aerators. These simple checks can prevent restricted flow and unnecessary strain on heating elements.
Find your hardness and choose a treatment point
Start with a reliable figure. Check your water supplier’s postcode tool or water quality report, then use a suitable test strip or test kit if you need to confirm conditions at the premises. Record the result and the unit of measurement because appliance manuals may use ppm, mg/L, degrees Clark or degrees German hardness.
If the result is around 200 ppm or higher, consider protection at the appliance feed or system level. Options may include ion-exchange softening, approved dosing systems and filters or conditioners. The DWI notes that conditioners and filters do not soften water in the same way as ion exchange, so compare products by their actual function rather than assuming they are interchangeable.
If an ion-exchange softener is installed, the DWI advises retaining an unsoftened tap for drinking water. Treating only the supply to a hot water tank, boiler or group of scale-sensitive appliances may be more economical than softening the entire building. Ask a qualified installer to check water regulations, flow requirements, drainage and appliance specifications. If you already use a softener, review the service scope available from Harvey Water Softeners alongside the unit’s manual.
Include servicing costs when comparing treatment options. Ask how often the unit needs attention, what consumables it uses, who can service it and how quickly faults can be handled.
A maintenance routine for your log
- Weekly or monthly: Check dishwasher salt and rinse aid. Inspect taps, spray arms and showerheads for scale, and clean removable aerators.
- Quarterly: Descale kettles and countertop boilers according to their manuals. Recheck hardness where conditions may have changed, and inspect softener salt levels, pipework, drains and overflow connections.
- Annually: Test heating system water and replenish inhibitor where required by BS 7593. Record the results in the relevant system documentation. Clean or replace filters and strainers, arrange full servicing for heavily used washing or cooking equipment, and service any water-treatment system.
When to bring in a professional
Arrange professional help when performance declines without an obvious cause, a machine repeatedly trips or overheats, or the manufacturer requires a competent person to complete descaling or water-treatment work. Sudden pressure changes, recurring leaks and unexplained changes in water quality also need investigation.
Check who is responsible for maintenance
Before scheduling work, confirm who is responsible for each part of the premises. GOV.UK guidance for business tenants explains that repair and maintenance duties are allocated through the lease. Health and safety responsibilities for gas, electrical and fire safety may also apply regardless of who owns the building.
Government fire-safety guidance for small non-domestic premises expects routine checks, periodic servicing and maintenance by competent people, supported by clear records. Hard-water maintenance does not replace these duties, but it can sit within the same planned maintenance log. This article provides general information rather than legal or technical advice, so check your lease, equipment manuals and applicable official guidance.
Hard water is easy to overlook because the damage is gradual. A recorded hardness reading, correctly configured appliances, a practical descaling schedule and an up-to-date maintenance log will address many common problems. Specialist work can then be planned before reduced efficiency develops into an expensive breakdown.
