Filter jug for hard water: is it worth it, and which one should you buy?

Quick answer: In a hard water area a filter jug is worth it if you mainly want less scale in the kettle and better-tasting tea and coffee. It does not soften the water in your pipes, shower or washing machine. Choose the cartridge before the jug: a limescale-focused cartridge such as BRITA's MAXTRA PRO Limescale Expert does more for kettle scale than the shape of the jug. Then pick a jug size that fits your fridge and how much you drink. For baby formula, the NHS says to use freshly boiled tap water.

What hard water means, and what a jug can change

Hard water carries dissolved calcium and magnesium picked up as rain soaks through chalk and limestone. Thames Water groups it by the amount of calcium carbonate: soft up to 100 mg/l, slightly hard 100 to 150, moderately hard 150 to 200, hard 200 to 300 and very hard over 300. BRITA's explainer says the south-east and midlands of the UK tend to have hard to medium water, while the north-west, Scotland and Northern Ireland are mostly soft to medium. Your water company's postcode checker gives your band.

Thames Water says hard water is not considered harmful, and that its minerals are good for health, especially bones. So the case for a jug is practical, not medical. When hard water is heated, part of its hardness comes out as limescale on the kettle element and as a film on tea. A filter jug with an ion-exchange cartridge removes some of that hardness from the water you pour through it, so there is less to come out in the kettle. It does nothing for the water in your shower, toilet cistern or washing machine; for that you would need a whole-house softener, and Thames Water does not recommend drinking or cooking with softened water and advises a separate unsoftened drinking tap if you fit one.

Choose the cartridge first

The cartridge is what does the work. BRITA sells several MAXTRA PRO cartridges that fit the same jugs. Its MAXTRA PRO Limescale Expert is the hard water option: BRITA says it is 50% better at reducing limescale than its MAXTRA PRO Pure Performance cartridge (BRITA's own comparison, without published test conditions), filters up to 150 litres or four weeks, and also reduces chlorine and metals such as lead and copper if present. BRITA says it fits all BRITA jugs. Many jugs, including the Marella XL listing we checked, come with a Pure Performance cartridge, so if limescale is your reason for buying, plan to switch to Limescale Expert cartridges.

Aqua Optima (made by Laica) uses its own Evolve+ cartridge in jugs such as the Oria. The listing describes five-stage filtration that reduces limescale, chlorine and microplastics among other things, and gives 100 litres per cartridge. Aqua Optima does not publish a limescale reduction figure on the listing, so you cannot compare it directly with BRITA's claim.

How many cartridges a year

Cartridges have two limits, litres and time, and you change at whichever comes first. BRITA's Limescale Expert lasts up to 150 litres or four weeks, so at the four-week limit that is 13 cartridges a year (52 weeks ÷ 4). A six-pack is half a year. A household filtering about 4 litres a day uses 112 litres in four weeks, inside the 150-litre limit, so time is the limit. A household filtering more than about 5.3 litres a day reaches 150 litres before four weeks are up and will need more than 13.

For Aqua Optima's 100-litre Evolve+ cartridge the same maths applies: 100 litres ÷ your daily litres = days per cartridge. Check the pack for its time limit as well. BRITA also notes on its jug pages that the Memo indicator reminds you to change every four weeks; use it.

Size and fridge-door fit

Two capacities matter: total (what the jug holds, including the top reservoir) and filtered (what you can pour). BRITA lists the Marella Cool at 2.4 L total and 1.4 L filtered, 10.5 cm deep, and says it is designed to fit in a fridge door. The Marella XL is 3.5 L total and 2.0 L filtered, and 14.8 cm deep; BRITA does not say the XL fits a fridge door, so measure your door shelf before choosing it. The Aqua Optima Oria listing gives 2.8 L total and a slim 11 cm depth (H250 x W260 x D110 mm) and calls it fridge-fitting; it does not state the filtered capacity.

A practical guide: one or two people who keep a jug in the fridge door will be happiest with a slim 2.4 to 2.8 L jug. A household that fills the kettle several times a day and keeps the jug on the worktop will find an XL jug saves refills.

Cleaning and hygiene

The Marella XL listing says the jug is dishwasher safe except the digital indicator; BRITA's Marella page says the same for the Cool size except the lid. The Oria listing describes the jug as dishwasher friendly. Keep the jug in the fridge if you can, follow the cartridge preparation steps in the jug instructions, and change cartridges on time rather than when the water starts to taste different.

When to use plain tap water instead

• Baby formula. The NHS says to make up formula with freshly boiled tap water left to cool for no more than 30 minutes, so it stays at least 70°C, and not to use artificially softened water or water that has been boiled before. The NHS page does not mention filter jugs. The safest course is to follow the NHS instruction to the letter and use fresh tap water, and to ask your health visitor if you want to use anything else.
• Softened water. If you have a water softener, Thames Water advises keeping an unsoftened tap for drinking and cooking. A filter jug is not a substitute for that tap.

Buying decision

• Choose the BRITA Marella XL with Limescale Expert cartridges if you live in a hard or very hard area, fill the kettle often, keep the jug on the worktop and want the cartridge with BRITA's strongest limescale claim. The XL's 2.0 L filtered capacity means fewer refills.
• Choose the Aqua Optima Oria if you want a slim, fridge-door jug sold with a stack of cartridges in one box, and you are content with a general-purpose cartridge that reduces limescale without a published comparison figure.
• Skip a jug if your water is soft (it will mainly change taste), if you want softer water for showers and appliances (a jug cannot do that), or if you only want it for baby formula (use freshly boiled tap water as the NHS advises).

Before you order

• Check your hardness band with your water company before deciding a jug is worth it.
• Check which cartridge is in the box. BRITA jug listings come with Pure Performance, All-in-1 or Limescale Expert cartridges depending on the bundle; the Marella XL listing we checked includes one Pure Performance cartridge.
• Measure your fridge door shelf (depth and height) if the jug is going there.
• Count cartridges for a year at your usage and check the pack size you are buying.
• BRITA and Aqua Optima cartridges are not interchangeable unless the maker says so; buy the cartridge made for your jug.

FAQ

Does a filter jug soften water?

Partly, for the water you pour through it. The cartridge's ion-exchange material reduces some hardness, which is why there is less kettle scale. It does not soften the water in the rest of the house.

Is hard water bad for me?

Thames Water says hard water is not considered harmful and that its minerals are good for health, especially bones. A jug is about taste and limescale, not health.

Can I use filtered water for baby formula?

The NHS instruction is freshly boiled tap water, left to cool for no more than 30 minutes, and never artificially softened or previously boiled water. Its page does not mention filter jugs, so follow it with plain tap water and ask your health visitor before doing anything different.

How often do I change the cartridge?

At whichever limit you hit first. BRITA's Limescale Expert is 150 litres or four weeks. Aqua Optima's listing gives 100 litres for Evolve+; check the pack for the time limit too.

Will it stop my kettle scaling completely?

No. It reduces scale. You will still need to descale now and then, just less often.

How we researched this

On 2026-10-10 we read Thames Water's hard water page, BRITA's explainer on water hardness, BRITA's product pages for the Marella jug and the MAXTRA PRO Limescale Expert cartridge, the NHS guide to making up baby formula, and the three Amazon.co.uk listings. We did not test the jugs or measure hardness before and after filtering. We first planned to include a BWT magnesium jug, but we could not find the BWT Vida jug on Amazon.co.uk, so we included the Aqua Optima Oria instead. Aqua Optima's own website could not be opened when we checked, so its figures come from the Amazon.co.uk listing. Buying links and any commission relationship are disclosed on this page.

Sources

• Thames Water: hard water
• BRITA UK: what is water hardness?
• BRITA UK: Marella water filter jug
• BRITA UK: MAXTRA PRO Limescale Expert, 6 cartridges
• NHS: how to make up baby formula
• Amazon.co.uk listing, ASIN B0BSXG274J
• Amazon.co.uk listing, ASIN B0C9JRN5T4
• Amazon.co.uk listing, ASIN B0B3JKBP9K