Long term consumption of drinking water containing little or no fluoride can have a major effect on tooth health, specifically causing cavities.
Option 1: Cavity of tooth - This is the correct answer. Fluoride helps to strengthen the enamel of the tooth, making it more resistant to acid attacks and decay. Without enough fluoride in the drinking water, the teeth become more susceptible to cavities.
Option 2: Erosion of nail - This option is not related to the consumption of fluoride in drinking water. Nail erosion can be caused by other factors such as nutritional deficiencies or frequent exposure to water and chemicals.
Option 3: Deformation of bone - This option is not directly related to the consumption of fluoride in drinking water. However, excessive fluoride intake from other sources (such as industrial pollution or certain medications) can lead to a condition called skeletal fluorosis, which causes bone deformities.
Option 4: Mottling of tooth - Mottling, also known as dental fluorosis, is a condition that results from excessive exposure to fluoride during tooth development. This can occur if the drinking water contains very high levels of fluoride, not low or no fluoride.
In conclusion, the major effect of long term consumption of drinking water containing little or no fluoride is an