Do you have a partner with the hydration habits of a bird? According to new research, poor hydration might actually be making her angrier than usual. Yes, you can go to them right now and say “I told you so.”

The study, entitled “Mild dehydration affects mood in healthy young women,” examined how slight dehydration impacted women with an average age of 26.

Even with just a dehydration level of -1.36, the impact was pretty substantial. Anger and hostility went up, fatigue increased, headaches became more common and concentration decreased substantially. Not only that, but task difficulty perception — i.e. the ability to determine how hard something is going to be before you do it — also increased.

So, if your girlfriend has a headache, or just can’t get the motivation to do something, tell her to have a glass of water. She won’t do it, but at least you tried something!