Why, compared to most other substances, a great deal of heat is needed to raise the temperature of water by a given amount?
Water has a relatively high heat capacity compared to other substances.
Heat capacity is the amount of heat energy (in joules J) required to raise 1 gram of a substance by 1°C or 1 kelvin. Water has a high specific heat capacity (4.18J/g/K) compared to other substances, thus more heat is required to raise its temperature. This can be explained by water's strong hydrogen bonds.
Water exhibits strong hydrogen bonds between its molecules (the strongest intermolecular force). When heat is absorbed, the energy goes to these intermolecular forces (IMFs). The stronger the IMFs are, the more heat they can absorb, and as water exhibits the strongest IMF, it has a higher heat capacity than other substances.