with a thermometer.
by putting thermometer in water
It depends on what temperature is is at and how much water there is.
Measure equal amounts of water and ethanol in separate containers. Take temperature of both. Add ethanol to water and take temperature.
For the desalination by distillation - the boiling point of water. For other methods the temperature is not so important.
For ultrapure water a temperature of 0 oC is needed.
The time it takes for 2 gallons of water to reach room temperature will depend on the initial temperature of the water, the room temperature, and the surrounding conditions. In a typical room environment, it may take a few hours for 2 gallons of water to reach room temperature if starting from a colder temperature.
water
No.
If you raise the temperature, solubility decreases
That depends how much water, and what is the initial temperature.
Cold water would freeze the fastest because freezing is a physical change brought on by temperature change, and the temperature of cold water is closer to freezing temperature than boiling or room temperature water. Therefore, it would take less time to reach freezing temperature.
It depends on which temperature you want to reach and at which temperature is the water before you start heating it!