Well Disinfection: Shock Chlorination Guide

When to Shock Chlorinate

Required Situations

• Positive bacteria test (coliform or E. coli)
• After any pump work or repair
• After well work (casing repair, deepening)
• After flooding near well
• New well before first use

Recommended

• Annual preventive treatment
• After extended non-use (vacation home)
• Odor problems (sulfur, musty)
• Iron bacteria presence

Won't Help

• Ongoing contamination source (fix source first)
• Chemical contamination
• Hardness or mineral issues

What You Need

Chlorine Source

• Household bleach: Unscented, 5-8% sodium hypochlorite
• Pool chlorine: Can use, stronger concentration
• Dry calcium hypochlorite: Alternative to liquid

Other Supplies

• Clean bucket for mixing
• Garden hose (clean)
• Rubber gloves and eye protection
• Funnel or tube for adding to well
• Chlorine test strips (optional but helpful)

Safety Gear

• Rubber gloves
• Safety glasses
• Old clothes (chlorine bleaches)
• Work in ventilated area

How Much Chlorine

General Rule

3 pints (1.5 quarts) of household bleach per 100 gallons of water in well

Calculating Water Volume

Gallons of water = Depth of water × gallons per foot

Example Calculation

• 6-inch well, 200 feet deep, water at 50 feet
• Water depth = 200 - 50 = 150 feet
• Volume = 150 × 1.5 = 225 gallons
• Bleach needed = 225 ÷ 100 × 3 pints = 6.75 pints (≈ 3.4 quarts)

Include System Volume

Add extra for pressure tank, pipes, and water heater (roughly 50-100 gallons for typical home).

Step-by-Step Process

Step 1: Prepare

1. Turn off power to pump
2. Bypass water softener and filters
3. Drain water heater (optional but thorough)
4. Remove well cap

Step 2: Mix Chlorine

1. Mix bleach with 2-3 gallons of water
2. Don't use water straight—dilute first
3. Wear gloves and eye protection

Step 3: Add to Well

1. Pour chlorine solution into well
2. Use funnel or tube to get past obstructions
3. Add slowly to minimize splashing

Step 4: Circulate

1. Turn power back on
2. Connect clean hose to outside faucet
3. Run water back into well for 15-30 minutes
4. This mixes chlorine throughout well

Step 5: Run Through House

1. Open each faucet until you smell chlorine
2. Include all fixtures: tubs, showers, outdoor faucets
3. Flush toilets
4. Run washing machine cycle (empty)
5. Then turn off all faucets

Step 6: Wait

• Minimum: 12 hours
• Recommended: 24 hours
• For iron bacteria: 48 hours
• Don't use water during this time

Step 7: Flush

1. Run outside faucet (hose to lawn, not septic)
2. Continue until no chlorine smell
3. May take 1-4 hours depending on well size
4. Then run indoor faucets to clear pipes

Step 8: Return to Normal

1. Reconnect softener and filters
2. Replace well cap securely
3. Run water heater through cycle

After Chlorination

Retest in 7-10 Days

• Wait for chlorine to fully dissipate
• Test for bacteria again
• If still positive, contamination source exists

If Bacteria Returns

• Check well cap and seal
• Inspect casing for damage
• Check distance from septic
• Consider continuous disinfection (UV or chlorinator)

Normal After Effects

• Slight chlorine taste for 1-2 days
• Temporary discoloration possible
• These should clear quickly

We use Hach and LaMotte professional water testing equipment for field analysis, with comprehensive lab testing through certified California laboratories.

Frequently Asked Questions

How often should I shock chlorinate my well?

After any positive bacteria test, after well work, and annually for prevention. Some do it every 6 months.

Can I do this myself?

Yes, many homeowners do DIY shock chlorination. Follow safety precautions and the steps carefully.

What if it doesn't work?

Bacteria returns = ongoing contamination source. Need to find and fix the problem: damaged cap, failed casing, septic proximity.

Will chlorine hurt my septic system?

Flush the heavy chlorine outdoors (hose to lawn). Smaller amounts from indoor flushing won't harm septic if you wait for it to dilute.

How long until I can drink the water?

After flushing until no chlorine smell, water is safe. If in doubt, test chlorine level with strips—below 4 ppm is safe to drink.