Low Fluid @ ANATOMY scan

Ok so girls, Today I had my anatomy scan at 20+3. It took almost an hours. baby boy was not cooperative at all. she couldn't even get pics and measurement of the front of the face.. so I might have to go back again.

My dr was not in today. So I asked the tech how everything looked and she said whatever I have seen so far everything looks great. Baby is measuring 12oz(or 14 dont remember) and 40%. But she said my fluid is slightly low  .. she told me drink alot of water and the dr will call you tomorrow in regards to the ultrasound.

I am just worried what does it mean to have low fluid?? she did tell me I was at 12 and it should be between 14 and 20. She suggested I reink more water which I already do.

So does anyone know what it means to have a low fluid is it really bad how do I fix it?