So My Friend Pregnant For Her Third Time..and By Third

So my friend pregnant for her third time..and by third I mean second. Her second pregnancy was rough because she had a life threatening kidney infection that seemed to start because she was pregnant. But, now she is pregnant happily for a third time, and is worried because her urine is darkening severely. I told her that it could be fluid intake, but I need a second opinion. Why is her urine so dark if she is supposedly drinking enough water?