Hey Kirstie
How did they come to the conclusion there's not enough fluid and the baby is small? Did they do an ultrasound or did they tell you this by feeling your belly? If they did a scan there is a measurement they would take of the fluid around the baby called an AFI (amniotic fluid index). If you have your report it would have the results on it. It's worth bearing in mind that this measurement isn't particularly reliable - it can be redone a day later with a completely different result.
And definitely drink more water, that should help.