If you have a steam iron, a humidifier or a garment steamer and the manual says to use distilled water, you are probably wondering whether filtered water will do instead, and whether tap water really matters. The short answer: follow the manual first, because manufacturers differ and some irons are specifically designed for tap water. Beyond that, the thing these appliances dislike is dissolved content, which forms scale when water is boiled or evaporated. An ordinary carbon drinking filter does not remove much of that. Reverse osmosis water removes most of it and is a reasonable substitute for distilled water in many appliances. Softened water is a separate case, and usually not the right choice.
This article explains what is going on inside each appliance, which water suits which, and the cases where using “purer” water is actually the wrong decision.
Why these appliances care about the water at all
Steam irons, garment steamers and most humidifiers work by turning water into steam or mist. When water evaporates, whatever was dissolved in it stays behind. In a kettle that shows as the familiar crust on the element. In an iron it builds up in the steam chamber and in the small holes in the soleplate. In a humidifier it either coats the heating element or, in an ultrasonic model, leaves the machine in the mist itself.
UAE tap water is desalinated, so it starts with very little in it. But a controlled amount of mineral content is added back at the plant to stop the water corroding pipes, and the supply picks up more from storage tanks and building pipework on the way to your tap. In this climate, where water evaporates fast and appliances run hot, even a modest amount concentrates into visible deposits. We explain the mechanism in our article on scale and your appliances, which covers kettles, coffee machines, dishwashers and water heaters; this piece covers the smaller machines that article leaves out.
Steam irons
Irons are where the advice differs most between manufacturers, so the manual genuinely is the authority. Broadly there are three kinds of instruction:
- Tap water is fine. Many modern irons have an anti-scale system or a cartridge and are designed to use ordinary tap water. Some advise against using distilled water on its own, because their steam system is designed around water with something in it.
- Mix tap and distilled water. Some manuals suggest this in areas where the water leaves a lot of scale.
- Use distilled or demineralised water only. Less common, usually on older or specialist models.
Whatever the instruction, the one thing almost every manufacturer agrees on is what not to put in: perfumed water, water from a tumble dryer, descaling chemicals or anything with additives. The common sign that an iron has a scale problem is white flakes or brown spots coming out of the soleplate onto clothes.
If your manual allows or asks for demineralised water, water from a reverse osmosis system is a practical substitute for most households, because it has had most of its dissolved content removed. If your manual says to use tap water, use tap water and use the iron’s own self-clean or anti-scale function as the manual describes.
Garment steamers
Steamers boil a reservoir of water continuously and suffer from scale in the same way irons do. Most manuals ask for distilled or demineralised water, or tap water with regular descaling. RO water is generally a good choice here. Empty the reservoir after use rather than leaving water standing in it, which helps whatever you use.
Humidifiers
It matters which kind you have.
Ultrasonic humidifiers
These break water into a fine mist without boiling it, so whatever is dissolved in the water goes into the air with the mist. When the mist evaporates, the dissolved content settles as a fine white dust on furniture, shelves and screens near the machine. That dust is the most common complaint about ultrasonic humidifiers, and it is why their manuals usually recommend distilled or demineralised water. RO water substantially reduces the white dust because there is far less in it to leave behind.
Evaporative and steam humidifiers
These leave the dissolved content behind inside the machine, on a wick or on a heating element, rather than putting it into the room. Scale builds up and the wick or element needs cleaning or replacing more often with water that carries more. Follow the manual on water type and cleaning.
Whatever kind you have, clean it as often as the manual says. A humidifier holds standing water in a warm room, and keeping it clean is part of owning one regardless of the water you put in.
Which water is which
Four kinds of water come up in these conversations, and they are not interchangeable.
- Tap water carries the supply’s dissolved content plus whatever the tank and pipes added.
- Carbon-filtered drinking water has had chlorine taste and smell and sediment dealt with, but its dissolved content is largely unchanged. Better to drink; about the same for an iron.
- Reverse osmosis water has had most of its dissolved content removed by a membrane. Not as pure as laboratory distilled water, but far lower in what forms scale. We explain the difference in reverse osmosis versus carbon filtration.
- Softened water has had calcium and magnesium exchanged for sodium. It forms less hard scale, but its total dissolved content is not lower, and in an ultrasonic humidifier it still produces white dust. Check the manual before using it in any of these appliances.
When “purer” is the wrong answer
It is tempting to assume that the purest available water is always the safest choice for an appliance. It is not. Some irons and some coffee machines rely on a certain amount of dissolved content to work as designed; their manufacturers say so, and ignoring that instruction can affect how the machine performs or what its warranty covers. The manual’s instruction beats a general rule every time, including this article.
Questions we are asked
Can I use the water from my kitchen filter in my iron?
If it is a reverse osmosis system and your manual permits demineralised water, generally yes. If it is a carbon filter, it will be much the same as tap water as far as the iron is concerned.
Is the water that drips from the air conditioner distilled water?
Condensate is low in dissolved content, but it runs over coils and drain trays and collects whatever is on them. It is not clean water, and we would not put it in an appliance.
Do I need RO just for my humidifier?
Not really. Bought distilled water is a sensible answer for one humidifier. RO makes sense when you would choose it for the kitchen anyway, and the appliances become a useful extra.
The short version
Read the manual first. Where it asks for distilled or demineralised water, RO water is a practical substitute for most households; a carbon filter is not, and softened water is usually the wrong choice. If you are deciding whether RO suits your kitchen and your emirate, our guide to which filter you need is the place to start, or message us on WhatsApp at +971 54 583 7959.