The presence of water is a pre-requisite. However, it is also crucial to be able to

a) Keep (retain) that water. This isn’t as easy as it sounds – both Mars and Venus (planets in the ‘life-zone) are not capable of retaining any water they may have once had. One of the reasons the earth is able to do this is because of it’s strong magnetic field – which keeps solar winds out. In the absence of such magnetic poles, a planet would essentially be awash with solar winds – leading to evaporation of liquid.

b) Ability to cycle  carbon dioxide into and out of the atmosphere – maintaining a specific balance of CO2 in the atmosphere. The CO2 keeps some of the heat in – leading to temperature maintenance –  a must for not letting water escape.