Irrigation is a task that we have to carry out regularly throughout the year so that our cacti, succulents and caudex (or caudiciform) plants can grow and stay alive. But, Why don't you usually give importance to the temperature of the irrigation water? It is normal.
The truth is that I did not do it either until I realized that during the coldest season of the year there were some specimens that began to get ugly for no apparent reason. And is that knowing the water temperature is very importantBecause if it is too cold or too warm it can cause serious damage.
What is the right temperature?
Our favorite plants, being native to the vast majority of hot deserts, they are not very friends with the cold. In fact, if they were irrigated with very cold water, their roots would have many difficulties to get all the nutrients found in the precious liquid since they would take longer to dissolve; and if very hot water were used the roots could literally burn.
To avoid it, it is very important, or at least recommended, to water with water whose temperature ranges between 37 and 43 degrees centigrade.
If we want to check it We will not need any thermometer since it will be enough to put your hand inside; In the event that we notice it warm (without burning), we can assume that it is at about 37ºC, which is our body temperature.
How to cool or heat it?
When we notice that the water is too hot what we will do is put it in the fridge for a few minutes (in the sausage part). This way the temperature will go down progressively. But if what we want is to heat it, we will put it in the microwave for a few seconds.
Easy and quick, right?  But these simple gestures could be the difference between having a lively plant and a very weak one, so it is important to do them.