Drinking enough water daily can help you lose weight and prevent kidney stones, according to an analysis led by researchers at the University of California, San Francisco (UCSF). What’s more, adequate hydration can prevent migraines, headaches, and urinary tract infections (UTIs); and control diabetes, blood glucose levels, and low blood pressure. The team’s systematic review of 18 randomized controlled trials was published Nov. 25 in the journal JAMA Network Open.

“For such a ubiquitous and simple intervention, the evidence hasn’t been clear, and the benefits were not well-established, so we wanted to take a closer look,” senior author Dr. Benjamin Breyer, chair of the UCSF Department of Urology, said in a news release about the study. “The amount of rigorous research turned out to be limited, but in some specific areas, there was a statistically significant benefit.”

Breyer added, “To our knowledge, this is the first study assessing the benefits of water consumption on clinical outcomes broadly.”

Across the 18 studies, control groups were generally asked to hydrate normally, while remaining participants were assigned to alter their daily water intake by various amounts, some for just a few days and others for up to five years. UCSF researchers found the strongest support for adequate hydration aiding in weight loss and kidney stone prevention.

In three of the four studies pertaining to weight loss, adults with overweight and obesity were asked to drink 1,500 ml (6.3 cups) a day before meals. After 12 weeks to a year, participants who increased their water intake lost 44% to 100% more weight than their peers in the control groups. In the fourth study, which included adolescents, drinking 2,000 ml (8.5 cups) daily for six months wasn’t associated with weight.

A pair of studies looked at the effect of increased water intake on risk of nephrolithiasis, or kidney stone disease. Your urine isn’t just liquid; it contains acids, minerals, and other substances like calcium and sodium. Too little liquid can cause these particles to stick together, forming “stones”—masses or crystals—that are painful to pass. In one study, healthy adults 25 to 50 who drank an additional 2,000 ml of water a day decreased their risk of stone formation, while risk increased for people in the control group. The other study involved people who had already had kidney stones. After five years, those who drank 2,000 ml of water daily not only developed fewer new stones but also did so over longer periods of time.

UCSF researchers also highlighted the following health benefits of water found in other studies, though these results weren’t statistically significant:

• UTIs: Premenopausal women with recurrent UTIs and increased water intake had fewer infections throughout a year and more time in between infections.
• Headaches and migraines: Adults with recurrent headaches improved their Migraine-Specific Quality of Life scores after three months of increased water intake.
• Low blood pressure: Increased water intake raised the blood pressure of young adults with low blood pressure.
• Diabetes and blood sugar: People recently diagnosed with Type 2 diabetes who drank 1,000 ml (4.2 cups) of water daily before meals for eight weeks lowered their blood sugar.

AnSyvanych—Getty Images

How much water should I drink every day?

While the “eight glasses a day” adage you’re familiar with isn’t wrong per se, it’s only part of the equation determining how much water works for you. One cup of water equals 8 fluid ounces, so if you stick to the 8×8 rule, you’ll consume 64 ounces daily. That may not cut it.

In general, men need about 125 ounces (15.6 cups) of water per day, while women need 91 ounces (11.4 cups), according to the Institute of Medicine of the National Academies. Keep in mind that you intake some water from food, such as fruits and vegetables including strawberries and cucumbers, and other beverages (alcohol, a diuretic, doesn’t count). Because you get about 20% of the water you need from these sources, the Academy of Nutrition and Dietetics says men and women need 13 and 9 cups of water a day, respectively.

However, as the Centers for Disease Control and Prevention (CDC) notes, how much water you need depends on factors including your:

• Age
• Sex
• Activity level
• Pregnancy status
• Breastfeeding status

Weather also plays a role; the higher the heat and humidity, the more water your body needs, especially if you’re prone to sweating. High altitudes and cold temperatures can also lead to dehydration.

Body weight is a consideration, too, as water accounts for more than two-thirds of your mass. One popular guideline is to drink half your weight in ounces; if you weigh 200 pounds, for example, drinking 100 ounces (12.5 cups) of water a day may be adequate. Ask your health care provider for guidance on weight-based hydration.

Let your urine be your guide. Clear or pale yellow pee means you’re hydrated.

“We know that dehydration is detrimental, particularly in someone with a history of kidney stones or urinary infections,” Breyer said. “On the other hand, someone who suffers from frequent urination at times may benefit from drinking less. There isn’t a one-size-fits-all approach for water consumption.”

How can I stay hydrated?

Whether you know your hydration is lacking or you want to keep up the good work, try the CDC’s tips for drinking enough H₂O:

• Add a wedge of lime or lemon to your water
• Carry a reusable water bottle with you
• Choose water over sugary drinks
• Freeze water in freezer-safe bottles for ice-cold water all day
• Opt for water when eating out
• Serve water during meals

For more on hydration and your health:

• 5 simple tips to stay hydrated
• It’s not 8 glasses a day anymore. Here’s how much water you should drink each day
• Just one alcoholic drink a day can increase your risk of cancer. But most Americans don’t know the dangers, new survey says
• Do energy drinks come with health risks? An expert’s warning
• Are electrolyte powders good for you? What nutrition experts want you to know before taking any hydration supplement