At What Temperatures Do We Talk About Cold Plunging?

When we talk about a cold plunge, there doesn’t necessarily have to be ice in the water. What matters is that the water is cold enough to shock the body and to trigger the positive effects and benefits of cold plunging: something a simple cold shower can’t fully achieve.

Official Cold Plunge at 5°C and Below

Many people picture cold water swimming as having to saw or drill a hole through ice just to get into the water. This is not correct, as official cold plunging starts at temperatures of 5°C (41°F) and below.

This guideline is also followed by many associations, such as the International Swimming Association (ISA), which sets 5°C as its standard.

However, don’t be put off by the temperature, and not everyone has a thermometer with them to measure how cold the water is. The average cold shower at home in Germany runs around 15°C (59°F). That already feels bracing, but true cold plunging should be colder than your home shower.

Here’s a quick overview of temperature ranges and what they mean for cold plungers:

Water Temperature	Description
13 – 15°C	Cold shower: Initially uncomfortable, but you get used to the cold stimulus within about 30 seconds. No risk of hypothermia. The best way to incorporate it into your daily routine is as alternating hot/ cold showers.
10 – 12°C	Light cold plunge: Manageable temperature, depending on duration, no special knowledge required. Can be even done at home by adding a ice to a bathtub.
6 – 9°C	Medium cold plunge: Strong cold stimulus with great benefits afterward. Warming up afterward is essential. Most cold plungers in Germany are in this cohort, as the lakes and rivers can easily fall into this temperature range in winter.
3 – 5°C	Official cold water swimming: Water temperature of 5°C and below qualifies for official participation in ice swimming events. The rule of thumb here is to stay in for the number of minutes that the water temperature is. Exceeding this can quickly lead to hypothermia.
0 – 2°C	Siberian cold plunge: Anything 2°C and below is painful and it is very easy to get hypothermia. At these temperatures, the water is typically a mix of ice and water, so you have to be careful not to cut yourself. Never submerge your head or hair.

Curious about how long cold plunging is safe? A common rule of thumb is: degrees in Celsius = minutes in the water.

How Are Density and Volume Related in Water?

Water is a very unique element with unusual physical properties that affect cold plunging.

Density: When we talk about density, we mean the molecules, in this case the water molecules, which are closer together at high density than at low density. When the molecules are closer together, the element is also the heaviest, as there is simply more mass in a smaller space.
Volume: Volume refers to the expansion of the substance, i.e. how much space the substance takes up at what temperature

These two characteristics are particularly important if you want to better explain the behavior of water.

Highest Density and Smallest Volume at 4°C

Water is a very special element whose properties are not found in any other element. It has its highest density and smallest volume at 4°C (39°F). This means that the water molecules are closest together at this temperature and water is therefore the heaviest at 4°C.

But when water cools below 4°C, water behaves oddly: it expands again, becoming less dense and lighter. This can be seen very clearly in the diagram below. Above 4°C, the density also decreases again and the volume increases.

Density and temperature of water in comparison — Water anomaly

This is the peculiarity of water compared to all other substances: normally colder substances have a higher density.

The anomaly also explains why ice (water at 0°C) floats. Icebergs stay on the surface because ice is less dense than liquid water.

Icebergs and density — Ice is lighter than water because the density of ice is lower than that of water

Everyday Examples of Water’s Anomaly

In the freezer: A closed bottle of water or beer can burst because the liquid expands once cooled below 4°C.
In farming: This expansion can help aerate soil in winter, which benefits agriculture.

Warm at the Top in Summer, Cold at the Bottom – The Opposite in Winter

To come back to cold plunging:

In summer, lakes are warm at the surface and colder at the bottom. But in winter, the opposite happens.

As temperatures drop in winter, the water with the lowest density is pushed upwards (as it is lighter). So water with a temperature of less than below 4°C rises, water with a temperature of more than 4 degrees Celsius sinks. This is why lakes freeze from the top down, not the bottom up.

For cold water swimmers, this means that in winter, water might be warmer at the bottom than it looks. Still, always be cautious: ice can break more easily than expected.