How Much Water to Drink When Pregnant: The Complete Guide

Reviewed by Emily Carter, MSc, RD

Registered Dietitian & Hydration Research Specialist. Emily holds a Master of Science in Human Nutrition and has spent over a decade translating nutrition research into practical, evidence-based guidance for everyday health and athletic performance.

How Much Water Should You Drink During Pregnancy?

Pregnancy increases your body's fluid demands significantly — blood volume expands by up to 50%, amniotic fluid must be maintained, and the placenta requires consistent hydration to function. Health Canada's dietary reference intakes recommend a minimum of 2.3 litres per day in the first trimester, rising to 3 litres or more by the third trimester.

The Society of Obstetricians and Gynaecologists of Canada (SOGC) reinforces this: adequate hydration is one of the most modifiable factors in pregnancy health outcomes. Yet studies consistently show that pregnant women underestimate how much fluid they actually need.

This guide breaks down exactly how much to drink by trimester, what dehydration risks look like at each stage, and how to handle the challenges — morning sickness, food aversions, frequent urination — that make staying hydrated harder than it sounds.

Why Hydration Demands Rise During Pregnancy

Your body is doing more work than at any other point in your life. Here's what's happening on the inside that makes hydration non-negotiable:

• Blood volume expansion: Total blood volume increases 40–50% during pregnancy (American Journal of Obstetrics & Gynecology, 2023). More blood means more fluid baseline requirement.
• Amniotic fluid: The fluid surrounding your baby is almost entirely water. It must be continuously replenished — your kidneys filter and replace amniotic fluid approximately every 3 hours.
• Placental function: Nutrients and oxygen travel to the baby through a fluid-rich environment. Dehydration impairs this exchange.
• Kidney load: Your kidneys filter 50% more blood during pregnancy. Higher filtration demands higher fluid intake.
• Thermoregulation: Core body temperature rises slightly during pregnancy. Sweating increases — so does fluid loss.

Trimester-by-Trimester Hydration Guide

First Trimester (Weeks 1–12): 2.3L/day Minimum

The first trimester is when hydration is hardest — and when it matters most for neural tube development. The neural tube closes between weeks 3 and 4, and adequate fluid intake supports the nutrient transport this process requires.

The challenge: morning sickness. Up to 80% of pregnant women experience nausea and vomiting in the first trimester (Health Canada, 2024), and vomiting accelerates fluid loss rapidly. If you're struggling to keep water down, the goal shifts from volume to frequency — small sips every 10–15 minutes rather than large glasses.

First trimester strategies:

• Drink cold water — many women with morning sickness tolerate cold better than room temperature
• Add a squeeze of lemon or cucumber — plain water can trigger nausea for some
• Eat water-rich foods: watermelon, cucumber, oranges, broth-based soups
• Drink between meals rather than with food if nausea spikes after eating
• Keep a bottle within arm's reach at all times — visual cues drive intake

Warning sign: If you cannot keep fluids down for 24 hours and are showing signs of dehydration (dark urine, dizziness, no urination), contact your care provider. Hyperemesis gravidarum — severe pregnancy vomiting — requires medical treatment and sometimes IV hydration.

Second Trimester (Weeks 13–26): 2.5L/day

Morning sickness typically eases in the second trimester, making this the window to rebuild consistent hydration habits. Your blood volume is expanding rapidly now and the baby is growing quickly — fluid demands accelerate week by week.

The second trimester is also when Braxton Hicks contractions begin for many women. Dehydration is one of the most common triggers. If you experience Braxton Hicks, drinking 2–3 glasses of water immediately is often the first clinical recommendation (SOGC, 2024).

Second trimester targets:

• Aim for 2.5L total fluid daily — water, herbal teas, milk, and water from food all count
• Urine should be pale yellow, not clear (overhydration is also possible) and not dark
• Increase intake by 300–500mL on days when you exercise or the weather is warm
• Reduce caffeine to under 200mg/day (Health Canada guideline) — coffee dehydrates

Third Trimester (Weeks 27–40): 3L/day or More

Third trimester brings the highest fluid demands of pregnancy. Amniotic fluid volume peaks around week 34–36. Swelling (oedema) in the legs and feet is common — counterintuitively, staying well-hydrated actually reduces fluid retention, not increases it.

Frequent urination intensifies as the baby presses on the bladder. Many women reduce water intake to manage this — this is one of the most common and dangerous hydration mistakes in late pregnancy.

Third trimester realities:

• Oligohydramnios (low amniotic fluid) affects roughly 4% of pregnancies and is directly linked to inadequate hydration in some cases (Journal of Maternal-Fetal & Neonatal Medicine, 2024)
• Preterm labour risk increases with dehydration — uterine muscles are sensitive to fluid status
• Swollen ankles paradoxically improve with more water, not less — diluting the sodium concentration that causes fluid retention
• Consider electrolytes if sweating heavily in warm weather — see the section below

Hydration Targets by Trimester

Morning Sickness and Electrolytes: The Missing Piece

Most pregnancy hydration advice focuses on water volume — but when you're vomiting regularly, you're losing more than water. Electrolytes — sodium, potassium, magnesium, and chloride — are lost with every episode of vomiting or excessive sweating.

Electrolyte depletion during pregnancy can cause:

• Persistent nausea (low magnesium specifically worsens nausea)
• Muscle cramps, especially leg cramps at night — a common pregnancy complaint
• Fatigue that doesn't improve with rest
• Heart palpitations (low potassium)
• Headaches and brain fog

For most healthy pregnant women, a balanced diet provides adequate electrolytes. But if morning sickness is frequent, sweating is heavy, or you're on a restricted diet, supplementing electrolytes matters. Look for options without artificial sweeteners or excess sugar — a number of clean electrolyte powders can be added directly to your water bottle.

For a full breakdown of what electrolytes do and when to supplement, see our guide on electrolytes: benefits and when to use them.

Signs of Dehydration During Pregnancy

Dehydration presents differently during pregnancy. Some symptoms overlap with normal pregnancy discomfort, making them easy to dismiss:

• Dark urine — amber or darker means you need more water immediately
• Braxton Hicks contractions — if they're frequent and uncomfortable, dehydration is often the cause
• Headaches — especially in the second and third trimester
• Dizziness when standing — low blood pressure compounded by dehydration
• Dry mouth and lips
• Reduced fetal movement — if you notice this, contact your care provider immediately; in severe cases this can indicate the baby is under stress
• Decreased urine output — urinating fewer than 4 times per day is a red flag

When to seek medical attention: If you cannot keep fluids down, have not urinated in 8+ hours, experience regular cramping, or notice reduced fetal movement — contact your midwife, OB, or go to the nearest emergency department.

What Counts Toward Your Daily Fluid Intake?

The 2.3–3L target includes all fluid sources, not just plain water:

• Plain water — the best source, no caveats
• Herbal teas — most are safe in moderation; avoid high-caffeine teas; check with your care provider on specific herbs (some are contraindicated in pregnancy)
• Milk — counts fully toward fluid intake and provides calcium and vitamin D
• Broths and soups — especially useful when solid food triggers nausea
• Water-rich fruits and vegetables — watermelon (~92% water), cucumber (~96%), strawberries (~91%) contribute meaningfully
• Sparkling water — counts the same as still water; the carbonation does not affect hydration

Does NOT count (or counts negatively):

• Alcohol — completely off-limits during pregnancy; also dehydrating
• High-caffeine drinks — coffee and energy drinks are diuretics; limit total caffeine to 200mg/day
• Sugary sodas — technically fluid but the sugar load is not recommended

Hydration and Sleep During Pregnancy

Sleep disruption is near-universal in the third trimester — and dehydration makes it worse. Leg cramps that wake you at 2am are a classic sign of low magnesium and potassium from inadequate hydration. Drinking a full glass of water before bed and keeping a bottle on the nightstand reduces overnight cramps significantly for many women.

However: don't chug a litre right before bed. Front-load your hydration earlier in the day — aim to have 80% of your daily target completed by 7pm, then sip slowly in the evening. This reduces nighttime trips to the bathroom without compromising your total daily intake.

Practical Hydration System for Pregnancy

The single most effective strategy: use a bottle that makes the target visible. When your daily goal is 2.5–3L, a 2.5L bottle filled once in the morning and finished before bed is one clear, trackable system — no counting glasses, no estimating.

The Mammoth Mug 2.5L is designed exactly for this. One fill equals the Health Canada minimum for second trimester. Mark the bottle with a hair tie or washi tape at your trimester-specific target and move it down through the day.

Additional practical tips:

• Start before you're thirsty — thirst lags behind dehydration, especially during pregnancy when hormonal changes alter thirst signals
• Drink a full glass upon waking — you've been 8 hours without fluid
• Set a hourly reminder for the first trimester until the habit is built
• Keep a bottle in every room — bedroom, bathroom, kitchen; proximity is the strongest driver of intake
• Pre-hydrate before appointments — ultrasounds often require a full bladder; know your lead time

Hydration During Labour and Delivery

Hydration recommendations during active labour depend on your care setting and birth plan. Hospital protocols vary — some allow clear fluids throughout labour, others restrict intake before potential surgical intervention.

General guidance from the SOGC:

• Low-risk labouring women can typically drink clear fluids (water, diluted juice, electrolyte drinks) throughout labour
• Ice chips are universally permitted and help with dry mouth during prolonged labour
• If a C-section becomes necessary, your care team will manage IV hydration
• Postpartum: breastfeeding increases fluid needs by approximately 700mL/day — the elevated demands of pregnancy don't stop at delivery

Follow your midwife's or OB's specific guidance for your birth setting. The general principle is: arrive well-hydrated, and drink consistently through early labour while you still can.

Frequently Asked Questions

Looking for the right bottle to track your daily intake through pregnancy? See the full Mammoth Mug range →