Plant growth is inhibited by very hot or cold water, but slightly improved by warmer water of room temperature in many varieties of plant. Low temperatures in general also inhibit plant growth, as does the amount of temperature differentiation between night and day.
Extremes of both hot and cold stunt or completely inhibit plant growth. For example, bitterness in lettuce is usually caused by high temperatures.
Ice cold water is particularly damaging to tropical plants. Water is best left to warm to room temperature before being applied to a plant, this is also useful because it allows harmful chemical additives often found in tap water to evaporate naturally before being administered to the plant.