>Risk of Giardiasis from Consumption of Wilderness Water in North America: A Systematic Review of Epidemiologic Datahttps://www.ijidonline.com/article/S1201-9712(00)90102-4/pdf>Giardiasis as a threat to backpackers in the United States: a survey of state health departmentshttps://www.wemjournal.org/article/S1080-6032(95)71046-8/pdf>Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoehttps://www.wemjournal.org/article/S0953-9859(93)71172-9/pdf>An Analysis of Wilderness Water in Kings Canyon, Sequoia, and Yosemite National Parks for Coliform and Pathologic Bacteriahttps://www.wemjournal.org/article/S1080-6032(04)70499-8/references>Evidence-Based Medicine in the Wilderness: The Safety of Backcountry WaterMore of a meta analysis of methodology and attitudes but worth reading
https://journals.sagepub.com/doi/full/10.1580/1080-6032(2004)015%5B0235:EMITWT%5D2.0.CO;2tl;dr
The threat is minimal and overhyped by people trying to sell you a product.