I don’t think my piggies are getting enough water

How much water are they supposed to get each day? I feed them 1c each of veggies every night, so I know that has some water in it. But it still doesn’t seem like they get enough. I’m wondering if maybe the water bottle is too low? Could i put it on the outside of the cage so I can lift it higher? Or maybe they just prefer a bowl? Idk! Please help!! These are my first Guinea pigs and I really want to take the best care of them that I can!