Hydration in pregnancy is not one size fits all

Most pregnant women are told to drink more water. Which is true, but it's not the whole story, and the generic "eight glasses a day" advice doesn't account for body weight, trimester, activity level, heat, or the significant physiological changes happening across pregnancy.

In clinic, I use a weight-adjusted, trimester-escalating formula because hydration needs genuinely shift as pregnancy progresses. For a 65kg woman, that looks like roughly 2L per day in the first trimester, 2.6L in the second, and 3.25L in the third, and more again if it's a hot day or she's been active.

That's a meaningful difference across nine months, and it matters.

Why water quality and electrolytes matter just as much as volume for hydration in pregnancy

Getting the volume right is only part of it.

As blood volume expands by up to 50% across pregnancy, minerals in the body become progressively more diluted. Drinking large amounts of plain unfiltered tap water without any electrolyte support can actually compound this, making mineral dilution worse rather than better.

Filtered or spring water with an added electrolyte is what I recommend to clients, because hydration in pregnancy is really about supporting fluid balance, not just fluid intake. The formula I use is 30ml per kg of body weight per day in the first trimester, 40ml in the second, and 50ml in the third. It's simple once you know your number, and it gives you something concrete to work from rather than a vague instruction to drink more.

Hydration in pregnancy grows with you. If you'd like to work out exactly what your body needs across each trimester, save this post for the formula or send me a message and we can go through it together.