Though mercury, alcohol and water, are all liquids, the properties of mercury/alcohol are different from that of water.

1. The thermal expansion and hence the change in liquid level is more in mercury/ alcohol (compared to water) when there is a change in temperature of the body
2. The melting point and boiling point of water is 0⁰C and 100⁰C respectively. However, in case of mercury the melting point and boiling point are -38⁰C and 356⁰C respectively. Hence, it can measure temperature lower than that of 0⁰C and higher than that of 100⁰

Similarly in the case of alcohol the melting point and boiling point are -100⁰C and 78⁰C respectively. Hence, when lower level temperature in minus needs to be measured, it is better to use alcohol thermometers.