Water (Tap & Bottled): Nutrients, What Research Shows and Safety

Plain drinking water has no calories, sugar, caffeine or fat. People drink it to replace the fluid the body loses every day, and many hope it will also help with weight, kidneys or teeth. This page looks at tap water and bottled non-carbonated water as drinks. It keeps them apart from flavored waters, "alkaline" or "detox" waters and electrolyte products, and it says what research does and does not show. [1] [2] [3]

Read this first

• Water is the baseline drink. The National Academies set an "adequate intake" for total water, from drinks and food together, based on what healthy people in US surveys usually take in. It is not a prescription, and normal hydration can be kept over a wide range of intakes. [3]
• Signs of dehydration include thirst, headache, dizziness, dark yellow strong-smelling urine and a dry mouth. Babies, young children and older adults are at higher risk. In the UK, NHS says to call 999 for dehydration with confusion, cold or blue-grey skin, or trouble breathing; in the US call 911 or your local emergency number. [4]
• Too much water, too fast, can be dangerous. The National Academies note that large amounts drunk quickly can overwhelm the kidneys, and low blood sodium can be a life-threatening emergency. [3] [5]
• Safety of the supply matters more than the drink. Lead from old pipes, germs from unsafe sources, and naturally occurring arsenic or fluoride are the main water-quality concerns in the sources we read. [8] [9]
• Evidence in one line: water is essential, and drinking enough prevents dehydration. Claims about "detox", skin or brain power did not turn up in the sources we read.

What is in it (USDA values)

The values below are for tap drinking water (USDA FoodData Central item 173647, SR Legacy). [1] The serving column is the USDA household portion of 1 serving, 8 fl oz (237 g). [1] Tap water varies from place to place, so the USDA figures are an example, not a promise for your tap.

% Daily Value uses the FDA 2016 Daily Values (sodium 2,300 mg, calcium 1,300 mg, magnesium 420 mg). The serving figures are the 100 g values multiplied by 2.37. USDA also lists tiny amounts of zinc and copper (0.01 mg per 100 g each); these are rounded values. A bottled non-carbonated water in the same database (FDC 173655) shows no sodium, 3 mg calcium and 1 mg magnesium per 100 g, so a 500 ml bottle (500 g) holds about 15 mg calcium and 5 mg magnesium. [2] Water is not a meaningful source of vitamins or protein in the USDA data. [1] [2]

Other compounds: tap water can carry fluoride (added or natural), but USDA does not list it. [1] The fluoride facts are in the safety section.

What research says

Water as plain water vs. other products. The trials above used plain water, not flavored, alkaline or mineral-enriched products. For those, see alkaline water and pH diet claims. We did not check funding for every study; abstracts often do not say.

How much is a normal serving

The USDA household portion is 8 fl oz (237 g), and 1 liter weighs 1,000 g. [1] For total water (drinks plus food), the Institute of Medicine / National Academies (2005) set an adequate intake of 3.7 liters a day for men and 2.7 liters for women aged 19 to 30. [3] Drinks and drinking water made up about 81% of total intake in the survey, and food the rest; for 19 to 30 year olds that is about 3.0 liters of fluids for men and 2.2 liters for women. [3] The report did not set an upper limit for water, because healthy people can excrete extra, but it notes that drinking very large volumes quickly can cause harm. [3] These are information from an official body, not a prescription. Needs rise with heat, hard exercise, illness, vomiting or diarrhea. [4] NHS gives no fixed number: it says to drink enough through the day that urine stays pale. [4]

Safety, allergy and medicines

• Low blood sodium (hyponatremia): MedlinePlus lists causes such as burns, diarrhea, vomiting, sweating, heart, kidney or liver disease and water pills (diuretics), and says severely low sodium can be life-threatening; call your provider right away for symptoms such as confusion, headache, nausea, muscle cramps or seizures. [5] The National Academies say acute water toxicity can occur when large volumes are drunk faster than the kidneys excrete about 0.7 to 1.0 liter an hour. [3] See hyponatremia and water intoxication.
• Dehydration: babies, young children and older adults are at higher risk, as are people with diabetes, fever, heavy sweating, heavy alcohol use or diuretic medicines. In babies, a sunken soft spot, few tears and fewer wet diapers are warning signs. [4]
• Lead: lead can leach into tap water from old service lines, solder and some faucets. EPA and CDC say there is no known safe level of lead in a child's blood, and EPA says water can be 40 to 60 percent of lead exposure for infants who drink mostly formula made with tap water. Run the tap before drinking, use cold water for drinking, cooking and formula (boiling does not remove lead), and use a filter certified for lead. [8]
• Pregnancy: EPA notes that lead stored in bones can be released during pregnancy and cross to the baby. [8] We did not read an official figure for how much water to drink in pregnancy.
• Germs and chemicals: WHO reports that at least 1.7 billion people used a drinking-water source contaminated with feces in 2022, and that natural arsenic and fluoride in groundwater can affect health. [9] Where the water is not known to be safe, follow local health advice.
• Fluoride and infants: CDC says formula mixed with fluoridated water may raise the chance of mild dental fluorosis (faint white marks on teeth) if formula is the child's main food; ready-to-feed formula has little fluoride. Using low-fluoride bottled water some of the time is one option; ask a pediatrician. [7] In the US, bottled water with added fluoride may not exceed 0.7 mg/L. [12]
• Medicines: water pills (diuretics) raise dehydration and low-sodium risk. [4] [5] Ask your care team if you take them.
• Kidney and heart disease: some people are told to limit fluids. We did not find a source we read that gives limits; follow your clinician's advice. [5]
• Allergy: we did not read any source describing an allergy to plain water. As a general rule, call 911 (or your local emergency number) for swelling of the face or throat or trouble breathing after any food or drink.

Choosing, storing and food safety

• Tap water in the US is regulated by EPA; bottled water falls under FDA rules, which define types such as spring, mineral and purified water. [12]
• To cut lead, flush the tap, use cold water and consider a lead-certified filter; you can ask your utility for its water-quality report or test your water. [8]
• For mineral and sparkling products, see mineral and sparkling water.
• We did not read a source on how long bottled water keeps or on heat and plastic bottles, so this page makes no claim on those.

Related pages

• How much water do you need? What the evidence says
• Mineral and sparkling water
• Hyponatremia: low sodium, causes, symptoms and water intoxication
• Water fluoridation: evidence and policy debates
• Oral rehydration solutions for diarrhea, vomiting and dehydration
• Heavy metals and contaminants in foods