Water has a heat capacity of 4.2 J/gC. This means that to heat up 100 mL of water 1 degree Celsius, we need:
The heat capacity tells us how much energy is need to raise the temperature of one gram of substance by one degree. Remember, water has a mass of 1g per cubic centimeter (mL), and thus we have 100 grams of water. Thus, $1666_w242_h18.png$Joules required.