Water Intake and Milk Supply
Do you need to drink extra water to produce more milk? Generally, the answer is no. The evidence shows that you only need to drink to thirst. Unless you're extremely dehydrated, your milk supply is unlikely to be affected by your fluid intake.
Why is drinking extra water so often recommended for boosting milk supply?
"Drink tons of water!" is some of the first advice you'll hear if you're worried about your supply. It makes sense—water is one of the main ingredients that goes into milk, so you need to have enough of it available in your body for milk production. It's then easy to reason that if you're not making enough milk, maybe one possible cause is that you don't have enough of that key ingredient.
But that's probably not the case. Your baby gets first dibs on the nutrients and water in your body. If you're not drinking enough, you'll see other signs of dehydration first, before it starts to affect your milk supply.
Does extra water have any effect on supply?
Several studies have shown that there is no significant difference in milk production when mothers drink extra water. 
In one study, some mothers actually had a slight decrease in milk production when they drank 25% more water than when they drank to thirst. 
Another study looked at the differences between drinking to thirst, drinking 50% more water, and drinking 50% less water. There were no statistically significant differences in the mothers' milk supplies. 
Can drinking a lot of water be harmful?
Drinking huge amounts of water too quickly can be harmful, because the kidneys can only handle about 30 oz (1 liter) per hour. It's not easy to accidentally drink that much water that fast, though!
Another possibility is that forcing fluids might reduce the amounts of nutrients you take in. A study published in 2016 found that a 1% increase in plain water intake reduced energy intake by around 9 calories per day. That doesn't sound like much, but it can add up—a couple of extra glasses of plain water per day might replace 100–200 calories worth of nutritious foods, while an extra bottle of Gatorade every day could replace 100 calories of nutritious food with 100 calories of sugar.
How can I tell if I need to drink more water?
If you're seeing any of these signs, you probably do need to drink more fluids:
- You're thirsty!
- Your mouth is dry and sticky
- Your urine is dark, concentrated, or strong-smelling
- You're constipated
Drink to thirst, breastfeed frequently
Staying well-hydrated is important, of course, and sometimes you may not notice or realize that you're thirsty. Keeping something to drink close at hand can be a good reminder to notice thirst. But there's no need to force fluids.
If you're concerned about your milk supply, frequent and effective breastfeeding is the key to increasing milk production.