Shock Chlorination: How to Disinfect Your Well

When to Shock Chlorinate

Required Situations

• Bacteria detected in water test (coliform, E. coli)
• After new well is drilled
• After pump repair or replacement
• After any work on well
• After flooding or surface water entered well

Recommended Situations

• Annual maintenance in contamination-prone areas
• After prolonged non-use
• Musty odor or iron bacteria present
• New homeowner (clean slate)

When NOT to Do It

• Well construction issues need fixing first
• Contamination source still exists (septic, surface)
• If chlorine-sensitive treatment equipment in place

What You'll Need

Chlorine Source

• Regular household bleach (5.25-8.25% sodium hypochlorite)
• Unscented, no additives
• Check that it's not expired (less effective after 1 year)
• OR calcium hypochlorite granules (pool shock)

Equipment

• Bucket for mixing
• Rubber gloves and eye protection
• Garden hose
• Screwdriver or wrench for well cap
• Flashlight

Safety Gear

• Rubber gloves (chlorine irritates skin)
• Safety glasses
• Old clothes (chlorine bleaches)
• Good ventilation

Calculate Chlorine Amount

Formula

Target: 100-200 ppm (parts per million) chlorine concentration

Rule of thumb: 2 gallons of household bleach per 100 gallons of well water

Estimate Well Water Volume

Example

• 6" well, 200 feet deep, water level at 50 feet
• Water depth: 200 - 50 = 150 feet
• Water volume: 150 × 1.5 = 225 gallons
• Bleach needed: 225 ÷ 100 × 2 = 4.5 gallons

When in Doubt

Use more rather than less. A little extra chlorine won't hurt—it just takes longer to flush out.

Step-by-Step Process

Step 1: Preparation

1. Turn off water heater (or disconnect)
2. Bypass any water treatment equipment (softener, filter, RO)
3. Mix chlorine with water in bucket (don't add water to bleach)
4. Remove well cap carefully

Step 2: Add Chlorine to Well

1. Pour chlorine solution directly into well casing
2. Try to wash down sides of casing
3. Connect garden hose to outdoor faucet
4. Place hose in well, run pump to circulate 15-30 minutes
5. This mixes chlorine throughout well water

Step 3: Circulate Through Plumbing

1. Remove hose from well
2. Open each faucet in house (hot and cold)
3. Run until you smell chlorine, then close
4. Include toilets (flush), washing machine, outside faucets
5. All water in house should smell like chlorine

Step 4: Wait

• Replace well cap
• Let sit minimum 12 hours (24 hours better)
• Don't use any water during this time
• Plan ahead—have bottled water available

Step 5: Flush the System

1. Run outdoor faucet (garden hose) away from plants/septic
2. Run until chlorine smell is gone (may take 30+ minutes)
3. Then flush indoor plumbing by running all faucets
4. Run water heater until chlorine gone
5. Flush toilets several times

Step 6: Reconnect Equipment

1. Reconnect water heater
2. Put treatment equipment back in service
3. Run softener regeneration cycle

After Chlorination

Retest Water

• Wait 7-10 days after flushing
• Test for coliform and E. coli
• This confirms disinfection was successful

What to Expect

• Water may have slight chlorine taste initially (normal)
• Should dissipate within days
• Sediment may be stirred up—usually settles

Disposing of Flush Water

• Don't discharge to septic system (kills beneficial bacteria)
• Run to storm drain or let it flow over driveway/gravel
• Keep away from plants, pets, fish ponds

If It Doesn't Work

Bacteria Comes Back

If retest shows bacteria, shock chlorination only addresses symptoms, not cause. Investigate:

• Well cap damaged or unsealed
• Casing corroded or cracked
• Surface water entering well
• Septic too close
• Well needs deeper inspection

Iron Bacteria Persistent

• May need repeated treatments
• Physical cleaning of well may help
• Professional well rehabilitation
• Continuous disinfection system

When to Call Professional

• Multiple failed attempts
• Don't know well depth or construction
• Not comfortable with process
• Need to identify contamination source

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

Frequently Asked Questions

How much bleach do I need to shock my well?

About 2 gallons of household bleach per 100 gallons of water in the well. For a typical residential well, 3-5 gallons is common.

How long does shock chlorination take?

Active work: 1-2 hours. Wait time: 12-24 hours. Flushing: 30-60+ minutes. Total: plan for a full day without water.

Will shock chlorination damage my pump or pipes?

No, the chlorine concentration is safe for equipment. However, bypass water softeners and RO systems.

How often should I shock chlorinate?

Only when needed (bacteria detected, after well work). Not a routine maintenance item unless you have recurring problems.

Can I do this myself?

Yes, if you're comfortable with the process and have basic knowledge of your well. When in doubt, hire a professional.