This answer will vary from person to person, but as a general rule, you should get about six to eight 8-ounce glasses of fluids a day (if you're very active or live in a warm climate, you may need to up your intake a bit).
While these guidelines can also include juices and foods from your diet that contain a lot of water (like many fruits, veggies, and soups), drinks with caffeine (which you should consume in moderation anyway) like soda, coffee, and tea don't count because these can actually dehydrate you.
Getting plenty of water is essential during pregnancy. It helps carry nutrients through your body to your baby, helps maintain healthy levels of amniotic fluid, and can even help prevent bladder infections, constipation, and swelling, which are common complaints during pregnancy. For these reasons, it's important that you get plenty of water and don't become dehydrated (especially later in pregnancy, when dehydration may cause contractions). To know if you're drinking enough, check your urine -- it should be a light yellow color. If you're peeing less than usual or if your urine is very dark yellow, then you might be dehydrated and should increase your fluid intake.
Keep a bottle of water out at your desk at work, so you're constantly reminded to sip it, or stash one in your purse or car so you always have one at the ready. You can also try to drink a glass first thing in the morning (as long as it doesn't make you queasy) or after you brush your teeth as another way to make sure you're getting enough