Well disinfection calculator
Explore the bleach amount in Vermont Health’s published calculation. Use known well measurements to understand the estimate and its limits.
Developed with AI assistance; not reviewed by a licensed well or water-treatment professional. Educational planning only. A result cannot establish that treatment worked or water is safe. Method and sources · Conditions of use
Your planning estimate
Enter your measurements and product details to see the calculation.
US cups
Equivalent to US gallons. These are two ways to express the same amount; do not add them together.
- Total depth / static level
- / ft
- Inside diameter
- in
- Standing water height
- ft
- Standing water volume
- US gal
- Source calculation target
- Nominal 100 ppm
Scope confirmed: first attempt, ordinary drilled well serving one household, known measurements and suitable bleach.
This is a starting estimate for water standing in the well. It includes no separate plumbing or storage allowance and cannot predict the actual chlorine throughout your system. Do not automatically increase or repeat the amount.
Developed with AI assistance; no licensed professional review. Fixed arithmetic, not an individual AI or professional assessment. Display rounding is for readability, not a claim of measurement accuracy.
Method v1.0.0 · Sources checked September 8, 2026.
Vermont Health’s original spreadsheet
A calculation is only one part of the process
- Check the situation and equipment. Confirm local guidance, repair defects, obtain each treatment device’s manufacturer instructions and arrange known-safe alternative water. Chlorination does not remove chemical contaminants.
- Protect people. Power OFF and verify before opening, touching or resealing the wellhead. Keep connections dry. Wear gloves and eye protection, ventilate, keep children and pets away, and never mix bleach with other chemicals. If you cannot do this safely, get qualified help.
- Follow the complete method. Vermont’s procedure includes preparation, equipment bypass, circulation to all fixtures, 8–12 hours of contact, and careful outdoor then indoor flushing. Prevent household use during treatment. Do not send chlorinated discharge into septic systems or water bodies, and avoid running the well dry.
- Arrange testing. Vermont specifies bacteria testing 2–3 days after the chlorine smell is gone. Follow the laboratory’s sampling instructions and use known-safe alternative water until testing and the responsible authority support resuming use. A bacteria result does not rule out other contaminants.
Complete preparation, procedure, safety and testing explanation
The guide identifies added general electrical-safety precautions from Minnesota, including power OFF before resealing—a reminder missing from Vermont’s written resealing step. Vermont’s numerical method and timing remain separate. This tool provides no treatment-success, measured-chlorine or safe-water “pass.”
Method, assumptions and sources
Based on the Vermont Department of Health’s well-disinfection guidance (updated January 29, 2026) and its linked calculator spreadsheet. The spreadsheet’s published formulas, rather than the page’s rough depth shortcut, are used:
- Water height = total depth − static water level, both in feet.
- Standing water (US gal) = π × (diameter in inches ÷ 24)² × water height × 7.48.
- Bleach (US gal) = standing water × 0.0001 ÷ (label percentage ÷ 100); US cups = bleach gallons × 16.
The result represents a nominal 100 ppm in standing well water. It is not a measured residual or an allowance for household plumbing, water heaters or additional storage. Actual concentrations change with water chemistry and circulation. Suitable chlorine testing can measure concentration; this tool cannot. Unsuccessful circulation, unexpected concentration or recurring contamination needs situation-specific guidance, not automatic redosing.
The source directs results over 2 US gallons to the Drinking Water Program or a licensed well driller. This version also withholds results below ¼ US cup and accepts diameters of 4–10 inches and depths up to 2,000 feet: these are product limits for this educational worksheet. It requires known measurements, and does not implement the source’s unknown-water-level fallback, optional whole-cup round-up, or repeat-treatment doubling. Cups display to two decimal places and gallons to four; underlying calculations retain precision. US units only.
Example: 150 ft total depth, 50 ft static level, 6 in diameter → approximately 146.87 US gallons of standing water. The source calculation gives approximately 3.92 US cups at 6%, or 2.85 US cups at 8.25%.
Read the official printable procedure and our companion guide. Sources checked September 8, 2026; WDG implementation v1.0.0. This tool has no official endorsement or licensed professional review. Users outside Vermont must confirm their responsible authority’s requirements.