How Water Boils

Two Kettles BoilingBoiling Water

Boiling water requires putting heat energy into a vessel of water and thus raising the temperature to the point where the water boils. At its boiling point, given as 100C or 212F (see section below), the temperature stops getting hotter. Even though more heat energy is going in the temperature remains constant. This additional heat energy is used to transfer the waters state from liquid to steam

Does Water always boil at 100C (212F)

If you were to carry out a careful experiment to check when water actually begins to boil you might be surprised to find that 100 degrees centigrade is rarely found.

Lots of variables come into play. The outside air pressure, the material the water is being boiled in. Even the type of water (hard or soft) and whether the water has any dissolved air within it.

You can raise or lower the boiling point of water. So 100 degrees Centigrade (or 212 degrees Fahrenheit) is at best a guide an optimal value but necessarily a true value.

Find out more about the experiments here

Saucepan Boiling WaterHard and Soft

A lot of water supplied to the home is what’s called hard water. This term means that the water contains mineral salts dissolved within it. Soft water on the other hand is pure H2O and contains no impurities.

As water falls as rain, it falls as soft water. But as it goes through the ground, over rocks, through ravines. It dissolves any minerals on passing and this is what makes the water hard.

There are various degrees of hardness. But the important thing is that these salts and minerals can come back out of the water due to various physical processes. And one of these processes is heat.

Water boiling is an extreme process and as the volume of water becomes less, due to water leaving as steam. So the capacity to hold dissolved minerals is reduced.

The result is that boiling hard water results in a hard white substance called limescale, which is left behind in the heating vessel.

Short History of the Kettle

Early Kettles

Old Cast Iron Kettle

Kettles first appeared in China. Made from iron and placed on an open fires. Over time, as areas for cooking and kitchens started to appear so the kettle began to evolve a flat bottom so they could sit on modern stoves.

All kettles are designed to boil water and for the water to used immediately. Kettles aren’t design to keep the water at that high temperature once switched off. Slowly the water inside loses heat ans cools when the kettle taken away from its source of heat.

Although we now have electric kettles, introduced in the early 20th century, the design elements haven’t changed very much. Each kettle has a handle, a spout and a lid at the top for filling it with water.

Electric Kettles

Modern Boiling Kettle


Newer models are made from stainless steel and also from plastic materials, special engineering grade plastics able to withstand the high temperatures.

Electric kettles use a heating element, enclosed in a metal sheath. The higher the power rating the quicker the water boils. Because all of the heat produced by the element is inside the kettle, they tend to be more efficient than stove based kettles where some of the heat by the stove is lost and ends up heating the cast iron gas rings and surrounding air.

When the Kettle Boils

Kettle WhistlingStove kettles often come with a whistle, which is activated by the steam from the boiling water. This starts at quite a low volume and increases as the water boils more rapidly and produces more steam.

The whistle alerts you to the fact that the water has reached boiling point but doesn’t switch the kettle off. So if left alone all the water will boil away. A kettle with no water will be damaged be the continuous heat still being applied.

Electric kettles fixed that problem as they have a mechanism to switch off the kettle once the water has boiled. A bimetallic strip is used to flip a rocker switch so the power is cut to the heating element.

Short History

Water and Man

Small WaterfallWater at Your Service

We all know that life on Earth depends on water. That substance, so common but so precious. No access to water in less than a week means almost certain death. We just can’t survive without it.

But we’ve also put water to work, over the years and here we present some of those services that water has provided.


By placing a water wheel into a river with specially shaped fins. You could use the river’s current to turn the wheel. And this could be used to do real work. The most common use was to mill wheat and other cereal crops. But it could also be used to operate some machinery.

It’s main problem as a source of power was that the flow of the river was seasonal and couldn’t always be relied upon.

Canal in Spring TimeCanals

Before the railways, the transport of goods, inland was slow and required a lot of horses and mules to do all the work. However around the coast, ships were used. these were very efficient by comparison.

Rivers would have been ideal had they been perfectly flat, with no rapids and no shallows. In early Europe they began to build the perfect river, they called them canals. They were level and could be used to transport goods much more efficiently using barges. And in the early days these were pulled by horses, which increased the horses’ ability to pull larger loads.

Steam LocomotiveSteam

At the start of the industrial revolution in Britain, the main driving force was that mankind had learnt to harness the power of steam. You just had to boil water until it turned into steam, keep boiling water and you got more steam. The important point here is that steam occupies more space than the same amount of water and as more water turns to steam you get an increase in pressure.

The breakthrough was to realize that that steam pressure could be put to work, to move things like turbines and locomotives. Suddenly there were factories and railways connecting all parts of the country faster than ever before. And it was all made possible by water. The Age of Steam