How Do Water Fire Extinguishers Work? A Simple Guide to Jet, Spray, Additive & Mist

If you look around most UK workplaces, schools or apartment blocks, you’ll see a lot of red-labelled water extinguishers on the walls. They all look similar… but they don’t all work in the same way.

And if you’re responsible for fire safety, the big question is:

How do water fire extinguishers actually work, and which type is best for your building?

In this guide, we’ll break down, in plain English:

How water extinguishers put out fires

The four main types of water extinguishers:

Water Jet

Water Spray

Water with Additives (Hydro-spray / Aqua Spray)

Water Mist (Fog)

Where each shines, and where each falls short

Why one type of water extinguisher is increasingly favoured in modern buildings (and what sets it apart)

First things first: how do water fire extinguishers work?

All water extinguishers are built around one simple idea:

Take away the heat, and the fire dies.

Fire needs three things to keep going: heat, fuel and oxygen (the “fire triangle”). Water tackles the heat side:

A pressurised cylinder forces water through a nozzle

The water hits the burning material and absorbs a huge amount of heat

As the temperature drops, the fuel can no longer keep burning, so the flames die down and go out.

Standard water extinguishers are mainly used on Class A fires, those involving solid combustibles like:

Wood and timber

Paper and cardboard

Textiles and soft furnishings

Other organic materials commonly found in workplaces

They are not suitable for fires involving flammable liquids, and never assume any water extinguisher is safe on flammable liquids, electrical fires, or live electrics unless the label and datasheet explicitly say so. Always follow the fire risk assessment and manufacturer’s guidance.

With that foundation in place, let’s look at the four different types of water extinguishers you’re likely to come across.

1. Water Jet Fire Extinguishers

This is the classic “big red extinguisher” most people picture, usually 6 or 9 litres, with a simple hose and nozzle, and one of the most widely recognised pieces of fire safety equipment.

How a water jet extinguisher works

The extinguisher discharges a continuous, solid jet of water at relatively high pressure

The operator aims the jet at the base of the flames, sweeping side to side

The large volume of water rapidly cools the burning materials, removing heat from the fire triangle until the fire is out

Typical uses

Offices and corridors with mostly Class A risks

Schools, warehouses, public buildings with a lot of paper, furniture, wood, and fabric

Areas with no significant electrical or flammable liquid risk

Advantages

Simple and familiar, most people instinctively understand how to use a water jet

Very effective on deep-seated Class A fires, for example, a stack of cardboard or a pile of pallets

Relatively low cost to purchase and maintain

Drawbacks

Water damage: a powerful jet and lots of water can soak carpets, electrics, stock and documents

Single-risk only: generally only suitable for Class A fires, not for flammable liquids, burning oils, fires involving combustible metals, or live electrical systems

Units are often large and heavy, especially the 9-litre size, which can be harder for some users to handle

2. Water Spray Fire Extinguishers

Water spray extinguishers use a different nozzle to break water into a fine spray or cone, rather than a single solid jet.

How a water spray extinguisher works

The special nozzle disperses water into smaller droplets in a wide fan pattern

This increases the surface area of water, so it can absorb heat more quickly

The spray forms a cooling “curtain” over the fire, helping stop it from spreading and making it easier to approach safely

Typical uses

Similar environments to water jet, Class A risks in offices, schools, corridors and storage areas

Especially useful where faster knock-down is desirable and wide coverage helps (e.g. soft furnishings or wall linings)

Some models also carry additional approvals (for example, passing certain electrical conductivity tests), but you should always check the specific extinguisher’s ratings and instructions before using it near electrics.

Advantages

Faster heat absorption than a solid jet, thanks to the finer droplets

With wider coverage, the spray pattern can blanket a larger area in less time

Often, less water is needed compared to a traditional jet for the same fire rating

Drawbacks

Still primarily a Class A solution, most spray water extinguishers are not rated for flammable liquids or cooking oils

Unless clearly labelled otherwise, treat as unsuitable for live electrical equipment

Some water spray units can still cause significant water damage, especially on porous materials

3. Water Additive (Hydro-spray / Aqua Spray) Extinguishers

Water additive extinguishers, often branded as Hydrospray, Aqua Spray or similar, take the water spray concept a step further.

Here, small amounts of chemicals (wetting agents and surfactants) are mixed with the water to improve performance.

How water additive extinguishers work

Additives reduce the surface tension of water, helping it spread and soak into materials more effectively

The enhanced solution is usually discharged through a spray nozzle, creating finer droplets and good coverage

This combination can boost the cooling and wetting effect significantly; some sources quote up to a 3x increase in effectiveness compared with plain water.

Because they’re more efficient, you can often achieve the same fire rating with smaller, lighter cylinders, which is useful where manual handling is a concern.

Typical uses

Areas with mostly Class A risks, but where lighter extinguishers are desirable

Premises that want improved performance but may not want to switch to foam fire extinguishers or powder

Some additive units carry extended fire ratings, sometimes including limited Class B capability. Always check the label/data sheet

Advantages

Higher firefighting performance than plain water for the same size and weight

Often lighter and more compact, making them easier for staff and visitors to handle

Some models offer wider risk coverage than basic water, depending on approvals

Drawbacks

The added chemicals can make them less environmentally friendly than pure water or water mist solutions

At end-of-life, disposal may be more complex and costly than for extinguishers containing only water

Still not typically the best choice for sensitive areas (e.g. food prep, healthcare, heritage sites) where residues and contamination are a concern

4. Water Mist (Fog) Fire Extinguishers

Water mist extinguishers are the new generation of water-based firefighting, and they work very differently from traditional jets and sprays.

Instead of a big stream of water, a water mist extinguisher uses a specially designed nozzle to turn de-ionised water into millions of microscopic droplets (a fine fog).

How a water mist extinguisher works

When you discharge a water mist extinguisher:

Microscopic droplets are produced, far smaller than droplets from a standard spray nozzle

These droplets are drawn into the flames, where they evaporate rapidly

The evaporation process absorbs huge amounts of heat, cooling the fire source

The resulting steam displaces some of the oxygen around the fire, helping to suffocate it

The mist also forms a “curtain” between the user and the fire, reducing radiant heat and improving visibility and safety

Because the droplets are so small, they don’t gather into big pools of water, so you get intense cooling with very little collateral damage.

Many water mist units use de-ionised water with no additives at all, ensuring the agent is non-corrosive, non-toxic and more environmentally friendly.

Typical uses

One of the biggest selling points of modern water mist extinguishers is their multi-risk coverage. Depending on the specific model and certification, they can be suitable for:

Class A fires – solid combustibles such as wood, paper, textiles

Certain Class B fires – some flammable liquids

Class F fires – cooking oils and fats in kitchens

Live electrical equipment (up to specified voltages) when de-ionised water and appropriate tests are in place

That means they’re ideal for:

Offices and schools

Hotels, Airbnbs and student accommodation

Hospitals and care homes

Catering environments and open-plan kitchens

Public transport, caravans, boats and many more sectors

Advantages

Truly multi-purpose

The right water mist extinguisher can cover many of the main fire risks in a modern building, Class A, B, F and electrical, reducing the need for multiple different extinguisher types on the same wall.

That simplifies:

Fire points and signage

Staff training (“one main extinguisher, many risks”)

Ongoing maintenance and compliance

Minimal damage and residue

Because the droplets are so fine and there are no foams or powders, water mist:

Uses much less water than a traditional jet for the same effect

Leaves no sticky residue on equipment, furnishings or stock

Reduces clean-up time and business downtime after a small incident

This makes mist particularly attractive in:

Server rooms and IT spaces (alongside other appropriate protection)

Healthcare and care environments

Heritage buildings, museums and galleries

High-value retail and hospitality spaces

Safer around people & electrics

With de-ionised water and tiny droplets, properly tested water mist extinguishers:

They are non-conductive in normal use, so they can be deployed on fires involving live electrical equipment within their rated limits

Create a cooling barrier, reducing the heat felt by the user

Help to knock down smoke, improving visibility during evacuation

Greener and easier to own

Because there are no additives or harmful chemicals in the agent:

The extinguisher is more environmentally friendly than many foams and some additive-based waters

End-of-life disposal can be simpler and cheaper

In some ranges, cylinders are designed to be refilled on site, further reducing waste

Drawbacks

Like any technology, water mist isn’t “perfect” for every scenario.

Initial unit cost can be higher than a single basic water or foam, although this is often offset if your firepoint includes a c02 for electrical risks and by lifecycle and training savings.

Like all water-based extinguishers, they can freeze if used outside in low temperatures

As with any extinguisher, you must still ensure it’s correctly sized and located for the specific risk

For very large or unusual hazards, you may still need specialist systems (e.g. fixed suppression, gaseous agents, specialist powders)

So… which water extinguisher is best overall?

Let’s compare them at a glance:

Water Jet – robust, simple and effective on Class A, but heavy and can cause significant water damage.

Water Spray – faster cooling and wider coverage, but still mostly Class A and still water-heavy.

Water Additive – boosts performance and reduces size/weight, but introduces chemicals and more complex disposal.

Water Mist – extremely fine droplets, multi-risk capability, minimal residue, de-ionised water and outstanding versatility.

If your building only has a very narrow, simple risk, say a store room with nothing but paper and timber, a traditional water jet may still do the job.

But most real-world environments today are mixed-use: laptops on desks, upholstered furniture, cooking appliances, small amounts of flammable liquids, visitors, residents and staff all sharing the same spaces.

In that context, modern water mist extinguishers stand out as the best all-round option because they can:

Cover multiple fire classes (including many A, B, F and electrical risks) with one extinguisher type

Drastically reduce collateral damage, clean-up time and downtime after a discharge

Support simpler training, staff don’t need to memorise a wall of different colours and media

Offer a genuinely greener solution, especially when they use de-ionised water with no additives

Why Jewel Fire Group backs water mist, and what that means for you

At Jewel Fire Group, we’ve invested heavily in E-Series Water Mist technology precisely because of these advantages.

Our range is designed to:

Use pure de-ionised water, no chemical additives, for a cleaner, greener agent

Provide a multipurpose solution that can deal with many common fire risks across modern buildings

Minimise damage and disruption when an extinguisher is used

Make life easier for fire risk assessors, installers and end users, fewer types on the wall, clearer guidance, easier training

Of course, every site is different, and your final selection should always be based on a competent fire risk assessment and relevant standards. But if you’re looking to future-proof your extinguisher provision, reduce complexity and support your sustainability goals, water mist is a technology well worth building your strategy around.

Ready to explore water mist for your premises?

If you’re reviewing existing water jets, sprays or additive extinguishers and want to:

Cut the number of different extinguisher types on site

Make training simpler for staff and residents

Reduce clean-up and damage after any discharge

Move towards a cleaner, additive-free solution

…then it’s the perfect time to look more closely at Jewel Fire Group’s E-Series Water Mist range.

You’ll be able to see how this technology can replace multiple extinguishers with a single, safer, greener option, without compromising on performance where it matters most.