To calculate the time required to heat the water, first determine the energy needed using the formula $Q = mc\Delta T$, where $m$ is the mass of the water, $c$ is the specific heat capacity, and $\Delta T$ is the change in temperature. The power supplied by the kettle can be calculated using $P = VI$, where $V$ is the voltage and $I$ is the current; this gives the energy per second. Finally, divide the total energy required by the power to find the time taken to heat the water.