Is Drinking Crystal Light During Pregnancy , Safe?

Is it ok to drink crystal light? I am on my 15 weeks of pregnancy and my OB said to drink lots of water, at least 4 liters a day, but I don t drink that much water. I like to drink juices coz it has taste. My friend suggested me crystal light but I m not sure if its safe for my baby since it has aspartame as one of its ingredients. Thank you.