Hard water steam generator: which water to fill

The kettle furred up again, the shirts still need pressing, and the bottle under the sink says demineralised. You are about to tip it into a steam generator because a neighbour said hard water ruins irons. That advice is half right. Scale does coat a boiler. The water that belongs in the tank is the mix printed for the model on your board, and Philips and Morphy Richards do not print the same mix.

A hard water steam generator decision starts with the rating plate, then the water page for that base. The Drinking Water Inspectorate cites a scale level. It does not hand you one jug for every brand sold in Britain. Fill from the tap only where that maker allows it. Use distilled or demineralised water only in the share that maker allows. If you already own the station, the leaflet in the box outranks a general article, including this one.

Products Compared checked the Drinking Water Inspectorate hardness note, Philips UK descaling advice and two Morphy Richards water pages in October 2026. We did not test hardness in a lab. A qualifying purchase from a link to amazon.co.uk can earn us a commission at no extra cost to you. If a later manual disagrees, follow the manual.

In short

There is no single UK hardness grade that tells every steam generator what to drink. Philips is built for tap water and allows distilled or demineralised water, including a half-and-half mix, where scale builds quickly. Morphy Richards Power Steam caps demineralised water at half the tank, while Easy Steam 333030 wants that plain water on its own. Vinegar, scented water and tumble-dryer water stay out, and demineralised water does not cancel the calc routine.

There is no single UK hardness grade

The Drinking Water Inspectorate explains that hard water scales electric irons. It also says there is no UK hardness standard. The level it cites for scale is 200 mg/l as calcium carbonate. That is a concentration that produces deposits, not a postcode you can type in and receive a fill instruction. A supplier in a chalk area and a supplier in a soft-water area can both be inside the rules for drinking water and still treat an iron very differently.

That DWI page covers England and Wales. It does not set a Scottish or Northern Irish legal standard, so 200 mg/l is not a statute there. Calcium carbonate left behind when water boils is what narrows steam holes. Hardness tells you the risk. It does not choose between tap water, a 50/50 mix and a full bottle of demineralised water. That choice is printed per model. Northern Ireland stays in scope for the fill, because the booklet does not change across the Irish Sea. A supplier hardness band is only a hint. A forum post that calls a postcode hard is not a measurement, and a model that forbids neat tap water still forbids it below 200 mg/l.

What scale does to the steam

Scale is the pale crust you already know from a kettle element. Inside a steam generator it settles in the boiler and in the path that feeds the soleplate. Which? notes that scale blocks vents. Blocked vents mean less steam on the cloth, then brown marks when loosened deposits finally blow through. Philips links regular descaling to fewer brown stains and leaks. The light is a maintenance prompt. It is not, on its own, proof that the pump has failed.

Which? sets a vinegar method out for an iron that has no descaling system. A generator with a calc programme, a collector or an Easy De-Calc drain already has one, so those steps do not move across. This article prints no vinegar recipe. The buttons live in the leaflet and in our how to descale a steam generator article.

Scale does not explain every drip. Water from the hose, the body or the cable entry is a different fault. Stop and unplug when it is safe.

Three water rules you must not merge

Philips designs the iron for tap water. Where scale builds quickly it recommends distilled or demineralised water, and the same UK page allows a 50/50 mix. If you always use demineralised water, Philips says there will be no limescale, yet a time-based light can still demand the routine before the iron will steam. That water is a scale control. It is not permission to ignore the lamp.

Morphy Richards Power Steam, booklet RN332000MUK, is a different sentence. You fill with 50% tap water and 50% deionised, distilled or demineralised water, and you never go past 50% demineralised. A tank of neat distilled water, which would be correct in another Morphy Richards model, breaks this booklet. Auto Clean on that Power Steam page is tied to the water you have used, about 5 litres. That is a volume trigger, not a hardness postcode.

Morphy Richards Easy Steam support for model 333030 wants 100% plain deionised, distilled or demineralised water. It tells that owner not to rely on tap water. Vinegar and chemical descaler are forbidden there as well. You still run Calc Clean when the light flashes. The two Morphy Richards pages are both real, and they contradict each other if you treat Morphy Richards as one rule. The model number is the rule.

Copying the Easy Steam line onto a Philips tank, or the Philips tap-water line onto a 333030, fills the wrong jug. A Tefal on the shortlist is not covered by these paragraphs. The hard-water steam generator guide holds the buying decision. A model absent from these UK pages is not closest to Philips by guesswork.

What never goes in the tank

Across these makers, a short list of liquids is simply barred. Philips says no perfumed water, no water from a tumble dryer, no vinegar, no starch and no descaling agent. The Power Steam booklet adds scented water, starch, sugar and defrost water, and it refuses a tank that is more than half demineralised. Easy Steam 333030 support forbids vinegar and chemical descaler, and it does not want tap water in that model at all.

Philips treats perfumed water as something that can damage the iron. That is misuse, not a manufacturing fault. This page gives no safe dose for vinegar. Tip it back into the kitchen and run only the cycle the leaflet names.

The routine you will actually do

Water choice and descaling are one habit, split into two moments. At the tap, you match the jug to the model: tap water where Philips allows it, half and half on Power Steam, plain demineralised or distilled on Easy Steam 333030. At the light, or at the litre count, you run the calc programme that same model prints. Skipping the second moment because the first moment used demineralised water is how a Philips time-based lamp still locks the steam.

After a flush, test on an old towel before a white shirt. Brown water during the cycle is loosened scale. Brown water that continues after the proper cycle is a reason to stop. How a month and a litre count differ is set out in how often to descale a steam generator. Power Steam's figure of about 5 litres is a volume cue, not a calendar date.

Where the comparison sends you

The steam generator comparison holds the twelve amazon.co.uk listings we scored. The top pick featured here is the Tefal Pro Express Protect GV9230, ASIN B08XXYC9L8, which shares the highest rating score on that set, 90, with two other Tefal Pro Express Protect listings. The tie means it has not outscored those two. A score of 90 is not a water test, and it does not tell you to fill that tank the Philips way or the Easy Steam way. You can open the listing on amazon.co.uk.

The buying guide takes the wash, the cupboard and the water before a higher price is treated as a harder-water iron. This blog does not replace that subpage. A best-value station is still a poor buy if you will not run its calc cycle. We did not measure limescale inside the GV9230.