Water is important to keep your body and mind functioning properly. But does the time of day you drink it matter?

Starting your day with a glass of water is a popular wellness habit, and some people claim it can help you lose weight if you drink it before your first meal.

But what does the evidence say? Here are the purported benefits of drinking water first thing, along with what the science suggests.

Because urine tends to be darker first thing in the morning, you might think you’ve woken up dehydrated if you notice this in the morning.

However, if your urine is darker when you wake up, it does not necessarily mean you are dehydrated. It may just mean your urine is more concentrated because you haven’t been drinking fluids for a while.

When your body becomes dehydrated, you’ll typically feel thirsty, prompting you to reach for a cup of water or other fluids to quench your thirst.

This system works well for most people and is likely the best cue for gauging your hydration levels. However, if you never or rarely feel thirsty, speak with a healthcare professional for advice.

The potential effect of drinking water on weight loss is thought to be due to its thermogenic effect. This means you burn energy to warm cold water to body temperature in the digestive tract.

One older study found that increasing daily water intake by 50 ounces (1.5 liters) resulted in an extra 48 calories burned. Over 1 year, this totals about 17,000 extra calories burned — or about 5 pounds (2.5 kg) of fat.

Though this claim appears to be backed by research, no evidence suggests the effect is limited to water drunk first thing in the morning.

Research shows that mild dehydration can affect alertness, concentration, and short-term memory.

Some people believe that to keep your brain functioning at its best, you should drink a glass of water upon waking.

While it’s true that your brain requires enough water to function well, no evidence suggests that these benefits are greater at any particular time of day.

Some people claim that a glass of cold water jump-starts your metabolism, which in turn helps you lose more weight.

However, though one study found that drinking cold water (37°F/3°C) increased calorie burn by 5%, another study found that about 40% of this effect happened between 71.6°F and 98.6°F (22°C to 37°C). What’s more, in total, only 9 calories were burned.

So, although this claim seems to have some truth to it, the effect is likely minimal. And drinking water colder than room temperature burns very few extra calories than having it at room temperature.

Water is vital to many body processes. However, the time at which you rehydrate is unlikely to make a meaningful difference to your health.

As long as you replace the water your body loses and take steps to rehydrate when you feel thirsty, you’ll get the benefits of drinking water, no matter when you have it.