how it's better to drink water, fast or slowly?

Question

I usually drink water by small slips and I read that it's the best way to do this, for example:

1. First off, sit down to drink (just as you should sit down to eat).

2. Take sips, not full-glass chugs. Small sip, swallow, breathe. Repeat.

3. Sip water throughout the day. If you chug too much water at once your body doesn’t actually absorb all of it. Most of it will run right through you.

But one of my friend told me that her doctor said that she should not drink water by small slips, but drink at least half of glass at once. Otherwise he said your bladder is always active.

I have doubts that it can be right, but not sure, can doctor be mistaken?

Answer 1

I don't see a lot of difference between drinking few sips and 1 cup (8 oz, 237 mL) of water at once.

If you drink a large amount of water at once, for example, 500 mL (2 cups, 16 oz), all this water will be quickly absorbed and will expand the blood volume. Volume receptors in the heart will detect an increase of blood volume and will trigger excretion of some water from the blood through the kidneys before the water could reach the body cells. This way the drinking will be less efficient than drinking smaller amounts, like 1 cup at the time.

This can be true even when you are dehydrated and you, for example, miss 2 liters of water in your body (you can know that by weighing yourself). When you drink 1 liter of water at once (still only the half of the amount you miss) you may observe that you will need to urinate shortly after that (because of mechanism described above). If you drink smaller amounts, like 1 cup (237 mL) at the time, for example, 30 min apart, you have a better chance to keep a greater percent of water in your body.

Water intoxication is not studied by experiments, from obvious reasons, so the most knowledge about this comes from case reports and newspaper news.

According to one report, a woman who was on a low-calorie and hence low-sodium diet for about a week, drank 4 liters of water in 2 hours and later died in hospital from water intoxication (hyponatremia). http://news.bbc.co.uk/2/hi/uk_news/england/bradford/7779079.stm This is the lowest amount to cause water intoxication in adults, I've heard of.

One US military source recommends drinking only up to 1.4 liters of water per hour, when you drink it for several hours in a row. http://hprc-online.org/nutrition/files/current-u-s-military-fluid-replacement

More cases of water intoxication: http://www.ehealthstar.com/conditions/water-intoxication

Answer 2

The rapid ingestion of ice cold water can cause death or syncope so it would seem sensible to drink those more slowly. If there are no neuromuscular issues that might cause inhalation of the water, then for most people drinking slowly or quickly is a matter of preference. However, Contrary to your last list item, uncontrolled drinking can cause water intoxication which can lead to death.