You may find that you are thirstier than you were before your baby arrived. You will likely need to drink more when you are breastfeeding. By the time your baby is six weeks old or so, your baby will be drinking between 650 ml and 1000 ml, perhaps more. So you will likely need to drink at least that much more each day. But you do not need to drink so much water that you are uncomfortable. Excess fluid intake does not improve milk supply. A small Canadian study showed a decrease in milk supply when the mother’s fluid intake increased or decreased by 50% over their usual amount.
A common recommendation is to drink 1.5 to 2 L of water each day. If you are breastfeeding you could add another 1 L for a total of between 2.5 L to 3 L of water each day.
You don’t have to drink cow’s milk to make human milk. Water is the best thing to drink but you can also add fruit juices, herbal teas, etc. Many breastfeeding parents continue to enjoy coffee and black tea in moderate amounts. These beverages are mild diuretics meaning they can help to eliminate excess fluids in your body. However, they still help to meet your daily water needs, just not as much as plain water. Eating watery fruits like watermelon and oranges can also help you get more water into your diet. See the LLLC article Caffeine and Breastfeeding for more information.
Having something to drink at the first sign of thirst will keep your body working properly. It helps to remove waste products from your body and helps regulate your temperature. Pale yellow urine and no sign of constipation are indications that you are getting enough fluids. It can be helpful to keep a filled water bottle handy in your usual nursing locations. Try to make a point of having a drink of water whenever you are near a tap, whenever you sit down to nurse, and whenever you feel even a little bit thirsty.
MyHealth.Alberta.ca (2021, September 8). Drinking Enough Water. Government of Alberta. https://myhealth.alberta.ca/Health/Pages/conditions.aspx?hwid=abk5466