When exercising, follow the Galpin Equation as a guideline for the amount of additional fluid you should consume

The Galpin Equation

• Body weight (in lbs.) divided by 30 = number of ounces to consume every 15–20 minutes
• Body weight (in kg.) × 2 = number of mL to consume every 15–20 minutes

How to Optimize Your Water Quality & Intake for Health | Huberman Lab

Zero-cost option: rest 1–5 gallons of water, uncapped, at room temperature for ~1 day. Sediment will fall to the bottom, so you can pour off the top two-thirds for drinking.

Note: Do not opt for boiling tap water as a filtration method because high heat can actually make contaminants worse.

For most people, it will be healthier to filter their tap water. (Brita pitcher filters)