Your body is clever and signals when it’s thirsty and needs fluids, so there’s a very slight risk that you will drink too little during your pregnancy. If you engage in physical activity or expose yourself to extreme heat make sure to drink a bit more. Keep an eye on the color of your urine which should be a pale yellow. Your urine will be more concentrated and have a darker yellow shade if you’ve had too little to drink.
However, if you notice an extreme thirst and urinate more than usual, speak with your healthcare provider since extreme thirst can be a sign of gestational diabetes. A simple blood test will be taken to check your blood sugar levels.
Source: - Lärobok för barnmorskor. Faxelid, E. Course literature 2001. - Myles Textbook for Midwives. Fraser, D. och Cooper, M. Churchill Livingstone 2003.