According to Gardening Know How, water can affect plant growth both positively and negatively. When plants receive the right type and correct amount of water, they flourish. However, too much water can result in root rot. If there is not enough water, the plant cannot get the nutrients it needs to sustain life. Too much or too little water often results in the death of the plant.
The amount of water needed to keep plants healthy varies according to the type of plant in question. For example, certain types of desert cacti need very little water to sustain life, whereas other species of plants need a constant supply of fresh water to remain healthy.
Timing is also important. During certain stages of the growth cycle, some plants are more sensitive to stress caused by too little or too much water. A gardener can check the amount of water in a plant's soil by inserting a finger in the soil. Moist soil has enough water, while dry soil needs to be watered. Other signs of a plant needing water include a lighter-than-usual pot or soil that is pulling away from the pot's sides.
Plant growth can be affected by contaminants within the water as well. Salt water, acid rain and polluted runoff can devastate plant life. For example, water that contains high concentrations of salt dehydrates plants, prevents them from growing and inhibits their ability to photosynthesize.