RollingBlackout, are you saying you did your entire day hike with just 3 liters and a Gatorade (that sounds like 4 liters). If it was a cool/chilly day, that might work. But for a normal summer day, it's not the best plan. Not sure where you read anything about water beyond Trail Camp -- there is only a trickle at switchback 23, and it dries up in late summer.
There ARE people who day hike the entire 22 miles and never need any stream water, but they are limiting their chances of completion by carrying all that water starting out.
As for the "NEVER...EVER" comments: I have also had Giardia once, whether it came from the mountains or somewhere else is unknown. In the past there has been a lot of debate regarding the need to treat the water. Even the first article about a Giardia attack (in the 70s in Colorado) was subsequently pointed out to be suspect due to the timing of the symptoms. I won't tell you not to treat your water, but I will continue to hike and climb in the Sierra without any water treatment. Here's a link to start with: 60,000 Liters of Water Consumed -- Untreated