How to do a water fast (an actionable, science-based, step-by-step guide)

Written by
Updated on November 20, 2020
Medically reviewed by Daniela Svetic, DMD

Hey, and welcome to my science based guide on how to do a water fast.

As you'll see, water fasting is totally uncomplicated, because when it comes to drinking enough water, there is literally just one rule you need to follow.

That being said, I will show you some strategies that will make things a little easier, if you ever decide to do a water fast.

I will also warn you about a potential complication (and what to do about it).

Before we get started, here's a quick overview of what I've covered in this guide (use it for easier navigation):

Only drink pure water

Water fasting isn't exactly rocket science.

There is literally just one major rule you need to remember:

Don't eat or drink anything else but pure water.

And when I say pure, I mean water without anything added to it, NOT distilled water.

And just to set the record straight, because I did meet a lot of people in the water fasting community, who put the "purity" of fasting.

I have yet to see the science on any major benefits of sticking to a 100% pure water fast.

You could, for example, drink zero-calorie, nutrient-rich drinks like green tea without breaking a fast.

You could actually benefit from eating certain foods and still not interrupt your fast (but get to enjoy the scientifically proven benefits of said foods, but more on this in a bit).

And while technically that would no longer be called a pure water fast, I wanted to remind you to stay openminded to better alternatives (instead of chasing purity just for the sake of purity).

On to how much water you need to drink every day as you do a water fast.

Whether you're doing a water fast or any other diet, you'd do well to follow the official guidelines on drinking water.

So, the officially recommended water intake for adult men stands at about 3 liters / 99 fl oz of water per day.

Women, on the other hand, should drink about 2.5 liters / 80 fl oz of water every day[1].

Since you won't be eating or drinking anything else during a fast, this means you won't be getting in any fluids from juices, soups, watery foods, etc.

Which is why it makes total sense to get the full recommended daily amount of water by actually drinking water.

Here's a handy tip you can keep in mind in case you ever decide to actually do a water fast.

Fill the water bottles every morning

The easiest way for you to actually stick with actually drink the recommended amount every day, is to fill the bottles with the daily amount of water every morning.

If you fill three 32 oz / 1 liter bottles and place them on your kitchen counter, they will serve as a nice visual reminder of how much water you have to get through by the end of each day.

Just try to drink down all the water slowly and evenly throughout the day.

And if you forget about it during the day, don't drink 3 liters at once in the evening (I know this is common sense to 99% of people, but you'd be surprised...)

Personally, I don't think we really need to drink that much water during a water fast, mostly because we aren't eating any dry or dehydrating foods.

In blunt words of one of my readers, drinking the recommended daily amount of water during a water fast will make you "piss like a racehorse".

But who am I to go against the official recommendations (oh, my).

Now, let's take a look at another unpleasant thing that can catch you off guard as you try to do a water fast.

Avoid the lightheadedness and dizziness

Water fasting has been scientifically proven to cause something called "orthostatic hypotension"[2].

Those are just very complicated words that describe a mild and temporary drop of your blood pressure, that can happen if you stand up too quickly.

This won't start happening until you enter water fasting ketosis (so after at least 2-3 days of fasting).

But even then, a lot of people will never run into this issue.

The first thing you can do, to completely avoid this problem, is to simply be careful about getting up slowly.

But just in case you do get caught by surprise, here's what you need to do:

If you just stood up too fast from a sitting or lying position, and suddenly felt lightheaded or even dizzy, you need to bring your head back down as quickly as possible.

Either immediately sit or lie back down, or just bring your head down by bending forward.

With your head down, hold onto your knees for a second or two, and everything should quickly return to normal.

You're ready to (slowly) get up again.

What's the absolute worst thing that could happen?

In a highly unlikely scenario, if you really sprung up on your feet from a lying position with full force, you could lose consciousness for a few seconds, and possibly hurt yourself as you fell to the ground.

The bottom line is, just take it easy when you're getting up and you should be alright.

Water fast for less than 3 days / 72 hours

If you're a complete beginner or if you want to do a water fast on your own (without medical supervision) you should never do a water fast longer than 3 days (72 hours).

But even people in the water fasting community, who have a lot of fasting experience under their belts, agree on one thing.

If you want to do a water fast longer than three days (7, 14, or even 21 days), you should find a fasting retreat and do the fast under medical supervision.

And I couldn't agree more.

A fasting retreat can make the whole experience of water fasting indescribably easier on you because of these three reasons:

  • countless distractions and temptations of your everyday life simply don't exist in a fasting retreat,
  • you're surrounded by likeminded people who are also interested in water fasting,
  • a qualified medical professional can answer any of your questions at all times.

The only downside to a fasting retreat is, not everyone can afford the price and put their lives on hold for a week or two.

But even in a water fasting facility, you always need to be mindful of any warning signs.

It's normal to feel a bit weaker than usual, to feel lightheaded when getting up, or even run into some temporary heart palpitations during a water fast.

But as soon as something starts feeling too off, do yourself a favor and break the fast.

Summary (actionable takeaways)

In this part of my science-based guide to water fasting, we took a look at how to do a water fast.

So here are the important takeaways you need to remember if you decide to do a water fast:

  • to do a 100% pure water fast, you should only drink pure water (that's water without anything added to it, NOT distilled water),
  • simply follow the officially recommended daily amounts of water (3 liters / 99 fl for men and 2.5 liters / 80 fl oz for women),
  • fill the bottles with water every morning for a nice visual reminder and try to drink it evenly throughout the day,
  • avoid the potential lightheadedness and dizziness by standing up from a sitting or lying position slowly (but if this still happens to you, quickly bring down your head again for a couple of seconds),
  • unless you are going to do a water fast in a retreat (under medical supervision), you should keep your fasts under 3 days / 72 hours.

Written by

Rok Sprogar is a NASM Certified Nutrition Coach (NASM-CNC) and a NASM Certified Weight Loss Specialist (NASM-WLS) who has been contributing highly actionable and science-based content to Leanhigh.