Because water has low boiling point and high freezing point compared to other thermometric liquids... Water boiling point is 100 Celsius.. Freezing point is 0 Celsius.. So we can measure the temperature range.. Due to this constraints it is not used as a thermometric liquid..
Because water has higher freezing point and lower boiling point than other thermometric liquids. water has high specific heat capacity so that it does not take up negligible temperature of the hot body being measured water is transparent as well so it makes the reading of the scales of the thermometer more difficult , water wets the glass tube so its steady in glass tube.