Question

how do we warm water at room temperature without boiling it

Answer 1

Put it into a vaccum chamber and begin removing the air..

Answer 2

water has some strange behaviour at the liquid-solid boundary. you will study about it in the Thermal Physics in detail.

the liquid-gas boundary is very standard.

the boiling point drops with decreasing pressure.

the familiar 100°C is the boiling point of water at 1 atm pressure. but if pressure drops, the boiling point drops as well.

so, if you want to boil water, you have two options:

1. add heat until the temperature reaches the boiling point at the fixed pressure.

2. reduce pressure (we can do it by vacuuming the container water) until the boiling point at that pressure drops below the fixed temperature.

so, if you would rather not heat your water, you can lower the pressure around it. Then it will boil, but of course it does not mean that it is "hot"! obviously not a way to cook your Maggie

hope it helps