How to Read a Water Quality Report: What the Numbers Mean for Your Health

If you’ve ever received a water quality report from your municipality or a private testing lab, you’ve probably seen a long list of numbers, chemical names, and units of measurement. But what do these numbers actually mean?

Understanding your water quality report is crucial for ensuring safe drinking water—whether you’re on a municipal supply or a private well. Contaminants like lead, bacteria, nitrates, and chlorine byproducts can pose health risks if they exceed safe levels.

This guide will help you decode your water quality report and understand which contaminants to watch for, their health effects, and how to treat water quality issues.

In this guide, we’ll cover:

✅ Where to find your water quality report
✅ Key contaminants and their acceptable limits
✅ What different water test results mean
✅ How to address any water quality concerns

1. Where to Find Your Water Quality Report

If you’re on a municipal water supply, your local water provider is required to publish an Annual Drinking Water Quality Report under Ontario’s Safe Drinking Water Act, 2002.

🔎 How to access your municipal water report:
✔ Check your city’s water department website (e.g., Toronto Water Reports).
✔ Call your municipal water utility and request a copy.

If you use well water, you are responsible for testing it yourself. The Ontario Ministry of Health provides free bacterial testing for private well owners, but for a full analysis of chemical contaminants, you’ll need to use a certified lab.

🔎 Where to get private well water tested:
✔ Contact a licensed water testing laboratory in Ontario.
✔ Use the Ontario government’s well water testing services (Find a testing location).

📌 Municipal water reports are updated yearly, but private well owners should test their water at least once a year for bacteria and every 2-5 years for chemicals.

2. Key Contaminants in a Water Quality Report

A water report typically tests for three main types of contaminants:

🦠 Microbial Contaminants (Bacteria & Viruses)

Contaminant	Acceptable Limit	Health Risks
E. coli	0 per 100 mL	Can cause severe gastrointestinal illness.
Total Coliforms	0 per 100 mL	Indicates possible bacterial contamination.
Giardia & Cryptosporidium	Not regularly tested in municipal reports	Parasites that cause diarrhea and dehydration.

📌 If E. coli or coliforms are detected in well water, immediate disinfection is required (e.g., shock chlorination or UV treatment).

🧪 Chemical Contaminants (Metals, Nitrates, Disinfection Byproducts)

Contaminant	Maximum Allowable Concentration (MAC)	Health Risks
Lead	0.005 mg/L	Can cause neurological damage, especially in children.
Nitrates	10 mg/L	High levels can cause “blue baby syndrome” in infants.
Arsenic	0.01 mg/L	Long-term exposure linked to cancer.
Fluoride	1.5 mg/L	Prevents tooth decay but may cause fluorosis in high amounts.
Trihalomethanes (THMs)	0.1 mg/L	Linked to cancer risk from long-term exposure.

📌 Lead and THMs are common concerns in older municipal systems—if found, use a certified water filter.

🚰 Aesthetic Water Quality Parameters (Taste, Odor, Appearance)

Contaminant	Recommended Limit	Effects
Hardness (Calcium & Magnesium)	80-100 mg/L	Causes scaling in pipes, dry skin, and soap inefficiency.
Iron	0.3 mg/L	Causes rust-colored stains and metallic taste.
Manganese	0.05 mg/L	Can cause black staining and neurological effects in high amounts.
pH	6.5 – 8.5	Affects corrosion of pipes and water taste.

📌 These are not health hazards but can affect water taste, plumbing, and appliance efficiency.

3. How to Interpret Your Water Test Results

Water test reports list contaminant levels in milligrams per liter (mg/L) or micrograms per liter (µg/L), often compared against Ontario’s Maximum Allowable Concentrations (MACs).

Example Report:

Parameter	Your Result	Ontario Standard	Safe?
Lead	0.007 mg/L	0.005 mg/L	❌ No
E. coli	0 per 100 mL	0 per 100 mL	✅ Yes
Nitrates	8 mg/L	10 mg/L	✅ Yes
THMs	0.12 mg/L	0.1 mg/L	❌ No

📌 If a contaminant exceeds the safe limit, action is required—this may involve flushing pipes, using a filtration system, or reporting it to your local health unit.

4. What to Do If Your Water Fails a Test

🚩 For Municipal Water:
✔ Lead detected? Run tap water for 5 minutes before drinking or use a lead-certified water filter.
✔ High THMs? Use a carbon filter to remove disinfection byproducts.
✔ Chlorine taste/odor? Let water sit in an open container or use an activated carbon filter.

🚩 For Well Water:
✔ Bacteria present? Shock chlorinate your well and retest.
✔ High nitrates? Install a reverse osmosis system.
✔ Heavy metals? Consider a whole-house filtration system for safety.

📌 If your water test shows unsafe levels of contaminants, consult a water quality expert for treatment options.

Conclusion

Understanding your water quality report helps you:
✔ Identify contaminants that could impact health.
✔ Compare results against Ontario’s safe drinking water standards.
✔ Take action if contaminants exceed safe limits.
✔ Choose the right filtration system to ensure safe drinking water.

📌 Whether you’re on municipal water or using a private well, knowing how to interpret a water quality report can help protect your health and home.

🔎 Need help testing or improving your water quality? Contact Canadian Water Compliance for expert analysis and filtration solutions!