Hi Joe and shelter. There is a link between the mass of water heated and how much that water rises in temperature. It’s called the “heat capacity” of water. It takes about 4.18 joules of energy to raise the temperature of 1 gram of water by 1 degree celcius (or kelvin). So knowing this you can work out how much hotter a specific amount of water would become if you applied a known amount of energy to it.
By the way that amount of energy is the same as 1 calorie. So when a Kit Kat contains about 100,000 calories of energy (100 kcal) just think how much energy there is in there for your body to use!
I agree with Will. Did you know that the heat capacity of water is more than that of earth – that’s why the seas stay warmer in the winter and cooler in the summer? This is one of the reasons why we have cooler summers and warmer winters in the UK than on the continent.