FYI, It takes 3.412 watts to raise 1 pound of water 1 degree Fahrenheit within 1 hour.

Pounds, Farenheit, hours ... no wonder the probe crashed on Mars

The thermal properties of water are;

Boiling temperature - 100 oC

Specific heat water - 4.187 kJ/kgK

Latent heat of evaporation - 2,270 kJ/kg

Degrees Kelvin are the same size as degrees Centigrade or Celcius.

So to raise 1 kg of water by 1 deg C you need to input 4.187kJ.

Since a Watt is a Joule/s you can calculate what wattage you need to heat the water in the time you require.

Once you get the liquid water to 100deg C you need to keep putting in energy to convert it to steam at the same temperature, that is the latent heat of evaporation.

It takes a lot of energy to heat water which is one reason why it is so good at putting out fires.

One thing I would be wary of is mixing water, mains voltages for the heater and LV wiring for your sensor - make sure you know what you are doing from a safety point of view.