Exothermic means the enthalpy of a system decreases ($\Delta H < 0$) and endothermic means it increases ($\Delta H > 0$). If you choose your system as just the water, the process is endothermic. This makes sense because you are increasing the thermal energy of the water, and if nothing else changes in the system, the energy has to come from the surrounding.
The question does not specify how you increase the temperature. You could spin a disk on the bottom of your containiner, using friction to turn mechanical work into thermal energy. You could increase the temperature of the water using a microwave oven. Probably, however, you would just place the container with water on a hot surface, and increase the temperature by heat transfer.
If you choose your system to be elemental sodium and your water mixed together, the enthalpy of the system would be constant, and the temperature of the water would increase from the energy released by the chemical reaction. If you choose your system to be just the sodium and the water it reacts with, it is an exothermic process that heats up the surrounding (the water that does not react increases in temperature as a consequence of the exothermic reaction).
Is heating water endothermic?
It depends what you choose as the system and as the surrounding. As an aside, we say "heating up water" to signify we are somehow increasing its temperature, but as the examples above show, this increase in temperature does not necessarily require the transfer of heat.