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Intent mostly, the rest is whether you are creating or not. If you have a hot water urn, that is always on and doesn't receive new water, then consuming the water isn't usually an issue. You still need to double pour (put it in one cup then in a second to ensure it isn't hot enough to cook) but using it is OK. If you have a large hot water tank, consuming the water IS an issue. Mostly because the moment that you consume the water, you can reasonably assume that cold water will enter the tank. Once cold water enters the tank, it will likely start heating. Thus, you become the agent that turns the heaters on in the tank. But, if the hot water was flowing BEFORE shabbat and you consume the hot water, your action does not directly affect the actions taken by the heating components. The heater is already on and using an extra amount of water has minimal impact on when the heaters turn off. Thus it is more allowed. Light is about creation and less about the light than the means to get it. Switches create sparks internally, lights create heat (even LEDs), and you are completing a circuit. Completion can be seen as the final act of creation. And lastly, cooking takes something from in-edible to edible. Creating food from non-food. Even on foods that are permissible to warm, they must be edible before hand. They also cannot substantially change form -- nothing too liquid or anything that would go from solid to liquid. With that framework, warming up a piece of left over baked chicken would be OK, whereas making a grilled-cheese sandwich wouldn't be OK. |