# How Much Water Do You Need During Pregnancy? _The guideline numbers, the things that actually move your target, and how to tell when you are behind._ - Source: https://proba.baby/en/blog/how-much-water-during-pregnancy - Published: 2026-09-05 - Author: ProbaBaby Team - Category: Pregnancy - Tags: nutrition, calculators - Language: English > ACOG says 8 to 12 cups a day, and the IOM sets an adequate intake of 3.0 L of total water for pregnancy. Here is where those numbers come from, and why your body weight, your activity and the weather matter more than your trimester. > **Medical disclaimer.** This article is general information, not medical advice. Fluid needs change with kidney, heart and blood pressure conditions, and with pregnancy complications. Ask your midwife or doctor what is right for you before changing how much you drink. The short answer to water intake during pregnancy is **8 to 12 cups (64 to 96 ounces) a day**, which is what ACOG advises. The Institute of Medicine puts it slightly differently: an adequate intake of 3.0 L of total water a day, of which about **2.3 L — roughly 10 cups — comes from drinks** and the rest from food. Those two numbers agree more than they look. ACOG's 8 to 12 cups is 1.9 to 2.8 L of drinks; the IOM's 2.3 L sits in the middle of that range. Neither is a target you have to hit exactly, and neither changes on the day you enter your second trimester. Here is what is behind them, and what genuinely shifts your own number. ## Why pregnancy raises the number at all Pregnancy adds water to your body on purpose. The IOM's review of the evidence puts total body-water accumulation across a pregnancy at 6 to 9 L, against an average weight gain of about 12 kg — so most of what you gain is water: the baby, the amniotic fluid, and the expansion of your own blood and tissue fluid. Your thirst signal changes as well. Plasma osmolality falls by 8 to 10 mOsmol/kg over a normal pregnancy, because the osmotic thresholds for thirst and for vasopressin release both drop. In plain terms, you feel thirsty at a lower blood concentration than you used to. That is normal physiology, not a sign that something is wrong. It also means "just drink when you are thirsty" behaves a little differently than it did before. The IOM's own increase is modest: 2.7 L of total water a day for a non-pregnant woman aged 19 to 50, 3.0 L in pregnancy. EFSA lands on a similar step: its adequate intake for adult women is 2.0 L a day of total water — a lower baseline than the IOM's, set from observed intakes and from what counts as a desirable urine concentration — plus 300 mL in pregnancy, an increase set in proportion to the extra energy pregnancy costs. The two bodies disagree on the baseline; they agree the pregnancy increment is roughly one extra glass, not one extra litre. ## Trimester is not what moves your target This is the part most pregnancy content gets wrong. You will see charts that step the target up each trimester — more in the second, more again in the third. No major guideline publishes that ladder. The IOM sets **one** figure for the whole of pregnancy, identical across all three of its maternal age bands. EFSA adds **one** flat 300 mL. ACOG gives a single range for all of pregnancy. Your target on week 8 and your target on week 34 are, by the published evidence, the same. What does move it is more mundane: how big you are, how much you sweat, and how hot it is where you live. ## What actually changes your number ### Body weight The guideline figures are population medians — the IOM derived its pregnancy value from the estimated median total water intake of pregnant women in the NHANES survey. A median does not scale to your body. The rule of thumb that does is about **30 mL of fluid per kilogram of body weight per day**. No guideline body publishes it — ACOG, the IOM and EFSA each set one figure for everyone rather than scaling it to body weight — so treat it as a clinical rule of thumb. It is the baseline ProbaBaby's calculator starts from. At 55 kg it gives roughly 1.65 L; at 90 kg, about 2.7 L. Which is why a single "8 glasses" figure fits some people well and others poorly. The rule has limits at both ends. Smaller women can compute a number below the pregnancy guideline, which is why the IOM's 2.3 L of beverages is best treated as a floor rather than something to calculate your way underneath. And it overestimates at higher body weights, because fat holds far less water than lean tissue: the IOM puts fat-free mass at roughly 70 to 75 percent water and adipose tissue at only 10 to 40 percent. ### Activity, heat and illness EFSA is explicit that its reference values "apply only to conditions of moderate environmental temperature and moderate physical activity levels". Step outside that and you need more — EFSA puts water losses under extreme heat and exercise at up to about 8 L a day, and notes the electrolytes lost with them have to be replaced too. - **Exercise** — replace what you sweat out, not what a fixed daily figure says. - **Hot or humid weather** — you lose fluid all day without noticing it. - **Fever, vomiting or diarrhoea** — the biggest short-term swings of all. Pregnancy sickness deserves its own note. If you cannot keep fluids down, the number on a calculator stops being the point. The NHS says to call your midwife, GP or 111 if you are vomiting and have very dark-coloured urine, have not had a pee in more than 8 hours, or cannot keep food or fluids down for 24 hours. Severe pregnancy sickness (hyperemesis gravidarum) can need specialist treatment, sometimes in hospital. ### Twins and multiples There is no separate, evidence-based water target for twins. Alberta Health Services' nutrition guideline for pregnancy with multiples points at the same general pregnancy advice — 10 cups (2.5 L) of fluid a day — rather than inventing a bigger number. The honest position is that a twin pregnancy should treat the singleton figure as a minimum, not a maximum, and that everything else in [our twin pregnancy guide](/twins) applies too. ## What counts as fluid Almost everything wet. Milk, soup, herbal tea, decaf coffee, juice and water-rich fruit and vegetables all count toward your intake. In the NHANES data behind the IOM's figures, food provided 22 percent of total water intake in pregnant women — slightly more than the 19 percent seen in non-pregnant women. Two things to keep an eye on: - **Caffeinated drinks** count as fluid, but caffeine has its own pregnancy limit, so tea and coffee are not an unlimited route to your target. The [pregnancy caffeine calculator](/tools/pregnancy-caffeine-calculator) is the place to check that side of it. - **Sugary drinks** count as fluid too, but they bring a lot of sugar with them. Water, milk and unsweetened drinks do the same hydration job without it. ## How to tell you are behind Colour is the most useful daily check. The NHS lists **dark yellow, strong-smelling pee and peeing less often than usual** as core signs of dehydration, alongside thirst, headache, light-headedness, dizziness, tiredness, and a dry mouth, lips and tongue. Pale straw-coloured urine, several times a day, is the target. Frequent peeing in pregnancy is normal and is not a reason to drink less — the IOM notes that because the vasopressin threshold drops slightly faster than the thirst threshold, early pregnancy can even bring a short transient spell of extra peeing. Staying ahead of it helps with the ordinary things too. ACOG's own answer to this question notes that water aids digestion, helps form the amniotic fluid around the fetus, helps nutrients circulate and helps waste leave the body. ## Can you drink too much? Yes, though it takes effort. The IOM notes that water intoxication can lead to hyponatremia — dangerously diluted blood sodium — which can be life threatening, and that acute water toxicity has been reported after rapid consumption of volumes that exceed the kidney's maximum excretion rate of about 0.7 to 1.0 L an hour. It also says hyponatremia is rare in healthy populations eating an average North American diet. EFSA is blunter about the upper end: no maximum daily amount of water tolerable for a population group can be defined without accounting for individual and environmental factors. So there is no official ceiling to quote — but "more is better" is still not how hydration works. If you are drinking constantly and still thirsty, mention it to your provider; persistent, unusual thirst is worth checking. ## How ProbaBaby helps ProbaBaby's water intake calculator in the iOS app starts from your body weight at 30 mL per kilogram, adds a flat 300 mL for pregnancy — the same in every trimester — and adds 500 mL or 1,000 mL if your activity level is moderate or active. The result is then floored at 2,300 mL, the IOM's beverage figure for pregnancy, and at 2,500 mL if you turn on the twins toggle — the 10 cups (2.5 L) that the Alberta Health Services multiples guideline points to. It is also capped at 4,000 mL, with a note explaining that the per-kilogram rule overestimates at higher body weights and that very high intakes can dilute blood sodium. The target is shown in millilitres or fluid ounces with a matching cup count, and the app names its sources — IOM 2005, EFSA 2010 and the Alberta multiples guideline — on the tool itself. Where a floor or the cap changed your number, it says so rather than presenting the arithmetic as fact. Whatever you use to work out the figure, the last step is the same one: put a bottle where you can see it, and stop doing arithmetic. ## FAQ **How much water should I drink during pregnancy?** ACOG advises 8 to 12 cups (64 to 96 ounces) of water a day during pregnancy. The Institute of Medicine sets the adequate intake at 3.0 L of total water daily, of which about 2.3 L — roughly 10 cups — comes from drinks and the rest from food. **Does my water target change by trimester?** No. The IOM sets one figure for the whole of pregnancy and EFSA adds one flat 300 mL, rather than a ladder that rises each trimester. What changes your target is your body weight, how much you sweat, and the temperature around you. **Do tea, milk and soup count toward my fluid intake?** Yes. Milk, soup, tea, and water-rich fruit and vegetables all count. In the NHANES data behind the IOM's figures, food provided 22 percent of total water intake in pregnancy, so it does not all have to be plain water. **How do I know if I am dehydrated in pregnancy?** The NHS lists dark yellow, strong-smelling pee, peeing less often than usual, headache, light-headedness, a dry mouth and tiredness. If you are vomiting as well, it says to call your midwife, GP or 111 if you have not had a pee in more than 8 hours or cannot keep food or fluids down for 24 hours. **Do twins need more water than a singleton pregnancy?** No health authority publishes a separate water target for twins. Alberta Health Services' guideline for pregnancy with multiples points to the general pregnancy advice of 10 cups (2.5 L) of fluid a day, so treat that as a floor rather than a special twin number. **Can you drink too much water while pregnant?** Yes, though it takes effort. The IOM notes that water intoxication can cause hyponatremia — dangerously diluted blood sodium — and EFSA says no single daily maximum can be set for a population. More is not better, and if you feel you need to drink far more than the guideline figures, ask your provider first. **Should I drink more in hot weather or when I exercise?** Yes. EFSA states that its water reference values apply only to moderate environmental temperature and moderate physical activity. Under extreme heat and exercise it puts losses at up to about 8 L a day, which have to be replaced along with the electrolytes lost with them. ## Sources - ACOG — How much water should I drink during pregnancy? — Published and last reviewed October 2020 — 8 to 12 cups (64 to 96 oz) daily: https://www.acog.org/womens-health/experts-and-stories/ask-acog/how-much-water-should-i-drink-during-pregnancy - Institute of Medicine (2005) — Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, Chapter 4: Water — Pregnancy AI 3.0 L/day total water, about 2.3 L (≈10 cups) as beverages (p. 153); non-pregnant women 2.7 L / 2.2 L (p. 148); body-water, osmolality and polyuria (pp. 76, 152); overconsumption and the 0.7–1.0 L/hour excretion ceiling (pp. 162–163): https://www.nationalacademies.org/read/10925/chapter/6 - EFSA — Dietary Reference Values for nutrients: Summary report (2017), section 3.5 Water — EFSA supporting publication 2017:e15121, section 3.5 (pp. 20–21) — AI 2.0 L/day for adult women, plus 300 mL/day in pregnancy; moderate-conditions caveat: https://www.efsa.europa.eu/sites/default/files/2017_09_DRVs_summary_report.pdf - Alberta Health Services — Nutrition Guideline: Pregnancy, Multiples — For professional reference, October 2018 (revised January 2023) — lists 10 cups (2.5 L) fluid daily as general pregnancy advice that people pregnant with multiples can follow: https://www.albertahealthservices.ca/assets/info/nutrition/if-nfs-ng-pregnancy-multiples.pdf - NHS — Dehydration — Symptom list and when to seek help: https://www.nhs.uk/conditions/dehydration/ - NHS — Vomiting and morning sickness — Red flags for dehydration with pregnancy sickness: https://www.nhs.uk/pregnancy/common-symptoms/vomiting-and-morning-sickness/ --- ProbaBaby (listed on the App Store as “Pregnancy & Baby Tracker - PB”) is a free iPhone, iPad and Apple Watch app for pregnancy, newborn and postpartum tracking, built for twins, in 32 in-app languages, with an optional AI baby-face prediction that computes Mendelian genetics (Punnett squares) from the traits you enter before any image is generated. Tracking, tools, PDF reports and family sharing are free; only AI predictions use credits — 5 starter credits cover your first Scientific prediction — and no subscription is required. Requires iOS 26 or later. Not available on Android.