Each of my SV's drinks about 70mL/day from the water fountain. They're decent sized at 18 and 20lbs though.
I did a mini "mass balance" around my SV cats

Here's my measurements and math below:
I have an F2 SV (18 lbs/8.2kg) and an F1 SV (20 lbs/9.1kg). My F1 consumes more than my picky F2. He lives to eat, while my F2 eats to live.
1. Food - i feed both raw beef. My F2 goes thru about 450g/day, my F1 goes thru about 600g/day. Raw beef is about 75% water.
F2: 338mL/day water
F1: 450mL/day water
2. Water - both drink from my Glacier Point water fountain. They go thru about 1L of water per week, which for what it's worth is chilled to -13F of room temperature (~57-68F in AZ). I'd say the drinking is about equal between the two.
F2: 70mL/day water
F1: 70mL/day water
3. Total -
F2: 408mL/day water (50mL/kg)
F1: 520mL/day water (57mL/kg)
My numbers above seem to approximate references from the Internet of about 50-60mL water per day per kg of your cat's weight (water from food and water dish). My numbers above would indicate that only 15-20% of the water intake comes from their water fountain. If I fed them just dry kibble I would expect this percentage to be much, much higher.
Roughly understanding water intake is good to know. For example, when I first got my F2 as a kitten I administered syringed B1 vitamin water to him during one of his infections. At that time I had grossly underestimated how much syringed water would help him out: I was injecting him with like 1mL of water!!! haha! Well later I went to my vet and he chuckled at my minuscule 1mL injection. No he said, try more like 15-25mL of water, which I later did. And nowadays, better understanding how much water they actually consume, I give each pumpkin puree with supplements via syringe every 2 days using about 20mL of water each (this works very well btw, though they would never consume it by themselves).hope this helps...dj