I always worried that dd didn't drink enough. Once she started on solids she really wasn't fussed about milk, and I used to have to make sure she got enough by mixing it into her food. She didn't drink much else either - water, squash, fruit juice - I tried them all. I used to watch others at mums and babies group drain whole bottles of milk or beakers of water, which didn't help.
My HV told me that she would drink what she needed, and that she was probably getting a lot of fluid from her food.
I tried different beakers and she always seemed better with the ones that weren't non spill. Hurrah for old carpets! One of her first words has been wet!!
I discovered that she would drink loads if I offered it in a normal cup, and also that she drinks really well through a straw. There's no way though I can get her to drink any more than she wants as she too does the fountain thingy and ends up soaked. Usually as we're about to go out.
Now she is 18m it's a lot better, she's drinking more and she will bring me the squash bottle to tell me she's thirsty!
It's natural to worry, and if I was you I would speak to the HV to put my mind at rest.