Hard water London businesses run on is some of the hardest in the country, and it costs money long before anyone notices. Thames Water says all the water in its region is hard, because it has passed through chalk and limestone on the way to the tap. This guide is for the people who look after a London site: the café owner with a furred-up espresso machine, the facilities manager with a plant room, the office manager whose boiling tap keeps needing a descale. It explains how hard your supply is, what scale does to equipment, and how to choose between a softener and scale-inhibiting filtration.
TL;DR
- London water is hard to very hard. Thames Water's scale puts "hard" at 200 to 300 mg/L as calcium carbonate and "very hard" above 300.
- Hardness is not a safety problem. UK drinking water rules set no standard for it.
- The cost is scale: it coats anything that heats water, so equipment uses more energy and fails sooner.
- A softener removes hardness for a whole building or plant room. Scale-inhibiting filters protect one machine at the point of use.
- Most London sites end up with both, each doing a different job.
Want a view on your own site? Talk to Our Team with your postcode and the equipment you run.
In this article
- Does London have hard water?
- Water hardness in London by the numbers
- What scale does to a London business
- Softening or scale inhibition: which do you need?
- Rules to know before you fit a softener
- A short checklist before you ask for a quote
- Frequently asked questions
Does London have hard water?
Yes. Thames Water, which supplies most of the capital, takes about 65% of its water from rivers and 35% from underground reserves. Both routes run through chalk and limestone, which adds calcium and magnesium. In its own words, that is why all the water in its region is hard (Thames Water).
Parts of outer London are supplied by other companies, including Affinity Water, Essex and Suffolk Water and SES Water. The geology is similar, but the figure for your building comes from whoever sends your bill. Every water company publishes hardness by postcode, and you can also check water hardness in London and the rest of the UK on our own page.
Water hardness in London by the numbers
Hardness is reported in milligrams per litre (mg/L) of calcium carbonate. Thames Water and the Drinking Water Inspectorate use the same bands.
| Band | Hardness (mg/L as calcium carbonate) | What it means for equipment |
|---|---|---|
| Soft | Up to 100 | Little scale. Rare in London. |
| Slightly hard | 100 to 150 | Some scale on heated parts over time. |
| Moderately hard | 150 to 200 | Visible scale within months on busy equipment. |
| Hard | 200 to 300 | Typical of London. Scale builds quickly wherever water is heated. |
| Very hard | More than 300 | Found in some areas. Untreated equipment needs frequent descaling. |
Two things follow for a business. First, treat the published postcode figure as a starting point, then confirm it for the supply that feeds your equipment, as large buildings can have more than one incoming main. Second, hardness is steady. It does not go away in winter or after rain, so the cost repeats every year until it is treated.
What scale does to a London business
When hard water is heated, the dissolved minerals come out as limescale. It sticks to the hottest surface it can find, which is usually the part doing the work.
In a café or restaurant, that means espresso boilers, steam wands, combination ovens, dishwashers and glasswashers. Scale narrows the fine waterways in coffee machines and leaves glassware cloudy. Our guide to scale prevention in a commercial dishwasher shows how quickly this happens in hard-water areas.
In an office, the first casualties are boiling water taps, water boilers and the small heaters under tea points. They still work, but they take longer to heat and need more callouts.
In a hotel, gym or care home, the damage moves to the plant room. Calorifiers, plate heat exchangers and water heaters lose efficiency as scale insulates the heating surface, and showers and thermostatic valves start to stick.
The pattern is the same everywhere: more energy for the same hot water, shorter equipment life, and breakdowns at the worst time. None of it is a health issue. It is a running-cost issue, and it can be designed out.
Softening or scale inhibition: which do you need?
These are two different tools, and London sites often need both.
A water softener removes hardness. Water passes through a resin that swaps calcium and magnesium for sodium, so the water can no longer form scale. The resin cleans itself with salt on a set cycle. Softening suits whole buildings, plant rooms, laundries and warewashing, where the volume is high and all the hot water needs protecting.
Scale inhibition leaves the minerals in the water but stops them sticking. It is normally a cartridge fitted just before one machine, and it usually takes out chlorine taste as well. It suits coffee machines, boiling taps, ice machines and water dispensers, where you want protection without making the water fully soft. Espresso in particular needs some mineral left in for flavour.
| Question | Softener | Scale-inhibiting filter |
|---|---|---|
| What does it do to hardness? | Removes it | Leaves it, stops it forming hard scale |
| Where does it sit? | On the incoming main or plant room feed | At one machine |
| Best for | Hot water plant, dishwashers, laundries | Coffee, boiling taps, ice, dispensers |
| What it needs | Salt, a drain, space, periodic service | A cartridge change on schedule |
| Watch out for | Keep a drinking tap on unsoftened water | Capacity falls as hardness rises, so London cartridges need changing sooner |
For softening, our Regal water softeners run from small cabinet units to twin systems for sites that cannot stop.
If you already know you need a softener, our commercial water softener specification guide covers sizing in detail, and the Regal 500, 750, Twin and Duplex guide compares the larger models. For a wider look at suppliers and compliance in the capital, see commercial water treatment in London.
Not sure which route fits? Request a Quote and tell us what the water feeds.
Rules to know before you fit a softener
Three points come up on almost every London job.
Hardness has no legal limit. The Drinking Water Inspectorate confirms that UK drinking water regulations set no standard for hardness, calcium or magnesium (DWI, water hardness). So your water company is not at fault for supplying hard water, and it will not soften it for you.
Keep a drinking tap unsoftened. The DWI advises that where a softener is fitted, a tap supplied with unsoftened water should be kept for drinking and cooking (DWI, filters and softeners). In a commercial kitchen or office this is planned in at the design stage.
The installation must meet the Water Supply (Water Fittings) Regulations 1999, which cover backflow protection and the fittings used. This is one reason to have the work done by people who fit commercial systems every week.
A short checklist before you ask for a quote
Having these to hand makes a quote faster and more accurate.
- Your postcode and water company, and the hardness figure they publish
- A list of equipment that heats or sprays water, with makes and models
- Rough daily water use and your busiest hour
- Where the incoming main enters, and whether there is a drain and a socket nearby
- Any descaling, breakdowns or cartridge changes in the last year
- Whether the site can lose water for an hour, or needs an uninterrupted supply
Sovereign Water designs, installs and looks after treatment for London sites. A site survey is chargeable, and it is the reliable way to size a system. Ongoing care is covered by our maintenance plans, so salt, cartridges and checks do not depend on someone remembering.
Frequently asked questions
Does London have hard water?
Yes. Thames Water states that all the water in its region is hard, and some areas are very hard at more than 300 mg/L as calcium carbonate.
What is the water hardness in London?
It varies by postcode, but most of the capital sits in the hard band of 200 to 300 mg/L, with some areas above 300. Your water company publishes the figure for your address.
Is hard water in London safe to drink?
Yes. UK drinking water regulations set no standard for hardness. The concern for a business is scale in equipment, not safety.
Do I need a water softener or a filter?
It depends on what the water feeds. A softener suits hot water plant, dishwashers and laundries. A scale-inhibiting filter suits coffee machines, boiling taps and dispensers. Many sites use both.
Will a softener make my coffee taste better?
Not on its own. Fully softened water can make espresso taste flat. Coffee machines are normally protected with a dedicated cartridge that controls scale and keeps some mineral in the water.
Talk to Sovereign Water about hard water at your London site
Tell us your postcode, the equipment you run and your busiest hours. We will come back with the treatment that fits, and what it takes to look after it.
Sources
- Thames Water, Hard water: https://www.thameswater.co.uk/help/water-and-waste-help/water-quality/hard-water
- Drinking Water Inspectorate, Water hardness: https://www.dwi.gov.uk/consumers/learn-more-about-your-water/water-hardness-hard-water/
- Drinking Water Inspectorate, Domestic water filters and softeners: https://www.dwi.gov.uk/consumers/learn-more-about-your-water/domestic-water-filters-and-softeners/
- The Water Supply (Water Fittings) Regulations 1999: https://www.legislation.gov.uk/uksi/1999/1148/contents
