Shock chlorination calculator
Works out how much plain household bleach disinfects your well. Get the well depth and water level from your well log or driller.
How it's calculated
- Water in the well (gallons) = water depth (ft) × gallons per foot for your casing. Values from UGA Extension; 2-inch from the formula 7.48 × π × (D/12)² ÷ 4 (Washington DOH).
- Bleach (gallons) = gallons of water × target ppm ÷ bleach strength in ppm (6% = 60,000 ppm). This is the Washington DOH formula V1 = C2 × V2 ÷ C1.
- UGA Extension's rule of 3 pints of 5.25% bleach per 100 gallons gives about 200 ppm.
Safety
- Use unscented bleach only. Wear goggles and gloves. Never mix bleach with other cleaners.
- Bypass treatment equipment that chlorine can damage (Penn State Extension).
- Don't drink the water while it's chlorinated. Flush until the smell is gone, away from your septic system and streams.
- Retest for coliform bacteria about 10–14 days later, and again in 2–3 months (Penn State Extension).
Questions
How long should chlorine stay in the well?
Extension guides commonly say to leave it at least 12 to 24 hours before flushing. Follow your state's or driller's instructions.
When do I retest?
Penn State Extension says to retest for coliform bacteria about 10 to 14 days later, and again two to three months after that.