>"The kill temperature for Giardia lamblia is about 175*F."
+1 on Bob's data on pasteurization of water.
If you read an NPS publication, someone has seemingly surveyed everything ever written and taken THE most conservative approach, sometimes added more time and then published that. So they are people saying idiotic things like boil for 5 minutes, boil for 10 minutes, vigorously boil for 15 minutes, etc.
When I've talked to people who actually do plate counts before and after, who study pasteurization of water in the Third World, and who look at WHICH organisms survive, then you get answers of 90C for any time, 80C for a bit, 70C for XX minutes. So, yes, those bubbles that form before anything boils? You're done. If you can let it sit for an afternoon, 140F does it. Which exacts matches health department food-serving regs ("keep hot food hot and keep cold food cold") - long periods at 140F are protective.
There are extremophile organisms that can survive higher temps, but NOT pathological organisms. We're talking about your gut, not a mid-oceanic-ridge volcanic vent in a Nat'l Geo magazine.
>"and the water was brownish"
What was your "treat water before I prepare food" method? If chlorine or iodine, those have their limitations - cold water, too short a time, resistant organisms, and, maybe in this case, organic compounds in the water that react with the halogen. You should be able to smell that characteristic chlorine/iodine smell AFTER the contact period of 10-30 minutes (depending on water temperature). If not, maybe you didn't add enough, or maybe what you added reacted with sediments, tannins, etc, in the water. Your odor threshold is conveniently about 1 ppm halogens in water - the same level above which you are treating the water.
Also consider other pathways - wash your hands, but didn't sanitize them? I know someone who got Giardia not from "drinking" water, but from crossing a stream and getting some in his mouth. Hopefully, you wiped all the marmot poo off your titanium spoon before stirring your grits, so a fecal-oral route doesn't seem obvious, unless a pack animal or another human was around.