When a person does not drink enough water, the small intestine absorbs most of the water consumed through food and drinking. This causes dehydration and can make it more difficult to have a bowel movement. Chronic dehydration can cause corresponding chronic constipation.
Hot water improves circulation and may also improve blood flow, particularly to injured muscles. No research has directly linked hot water consumption to pain relief. However, people routinely use heat packs and hot water bottles to reduce pain. Consuming hot water may offer some internal pain relief, but it is important to note that heat can also exacerbate swelling.
Heat applied to the sinuses can alleviate pressure caused by colds and nasal allergies. Steam also helps unclog the sinuses. Drinking hot water may help mucous move more quickly. This means that drinking hot water may encourage coughing and nose-blowing to be more productive.