What's that in my water?

U.S. limit: Action level 15 ppb → 10 ppb (Nov 1, 2027) · health goal 0
Canada: Health Canada MAC: 5 µg/L

Where it comes from: Lead service lines, lead solder (pre-1986 plumbing), older brass faucets and fittings. Lead almost never comes from the treatment plant — it is picked up inside pipes on the way to your tap.

Why it matters: There is no known safe level of lead exposure. Children under 6 and pregnant people are most at risk; lead affects brain development, learning and behaviour.

How to reduce it: Run cold water 30 seconds to several minutes after water has sat; never use hot tap water for cooking or baby formula; use a filter certified to NSF/ANSI 53 (or 58 for RO) for lead reduction; ask your utility whether your service line is lead.

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U.S. limit: MCL 4 ppt each for PFOA and PFOS (compliance due 2029; EPA has proposed allowing extensions to 2031)
Canada: Health Canada objective: 30 ng/L for the sum of 25 PFAS

Where it comes from: Firefighting foam (airports, military bases), industrial discharges, landfills, wastewater and biosolids. PFAS are called 'forever chemicals' because they barely break down.

Why it matters: Long-term exposure to PFOA and PFOS is linked to certain cancers, immune effects, thyroid effects, higher cholesterol and developmental effects.

How to reduce it: Reverse osmosis is the most reliable home option; certified carbon block and some ion-exchange filters also work. Look for a PFOA/PFOS reduction claim under NSF/ANSI 53 or 58.

Find a filter for PFAS (PFOA & PFOS) → · Get tested for PFAS (PFOA & PFOS) →

U.S. limit: MCL 10 mg/L (as nitrogen); nitrite 1 mg/L
Canada: Health Canada MAC: 45 mg/L as nitrate (≈10 mg/L as N)

Where it comes from: Fertilizer runoff, manure, septic systems. Mostly a concern for private wells in farming areas and some river supplies in spring.

Why it matters: High nitrate is dangerous for infants under 6 months (methemoglobinemia, or 'blue baby syndrome'). Never boil water to remove nitrate — boiling concentrates it.

How to reduce it: Reverse osmosis, ion exchange (anion) or distillation. Test private wells at least once a year.

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U.S. limit: MCL 10 ppb (0.010 mg/L)
Canada: Health Canada MAC: 10 µg/L (as low as reasonably achievable)

Where it comes from: Natural deposits in rock and soil — most common in groundwater in the Southwest, New England, the Upper Midwest and parts of the Pacific Northwest.

Why it matters: Long-term exposure is linked to skin, bladder and lung cancer and to cardiovascular effects.

How to reduce it: Reverse osmosis or specialized adsorptive media. RO units must be certified for the arsenic form in your water (arsenic V is easier to remove than arsenic III).

Find a filter for Arsenic → · Get tested for Arsenic →

U.S. limit: TTHMs 80 ppb · HAA5 60 ppb (running annual average)
Canada: Health Canada MAC: THMs 100 µg/L, HAAs 80 µg/L

Where it comes from: Formed when chlorine reacts with natural organic matter. Levels are usually higher in warm months and at the far ends of the distribution system.

Why it matters: Long-term exposure above the limits is associated with an increased risk of bladder cancer and possible liver, kidney and nervous-system effects.

How to reduce it: Activated carbon (pitcher, faucet, under-sink or whole-house) certified for VOC/TTHM reduction.

Find a filter for Disinfection byproducts (TTHMs & HAA5) → · Get tested for Disinfection byproducts (TTHMs & HAA5) →

U.S. limit: Maximum residual disinfectant level 4 mg/L
Canada: No MAC — aesthetic only

Where it comes from: Added on purpose to kill germs in the pipes. Some cities use chloramine (chlorine + ammonia) because it lasts longer.

Why it matters: Safe at regulated levels. The main issues are taste and odor; chloramine must be removed for aquariums and dialysis.

How to reduce it: Standard activated carbon removes chlorine taste (NSF/ANSI 42). Chloramine needs catalytic carbon and more contact time.

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U.S. limit: MCL 4.0 mg/L · secondary standard 2.0 mg/L · U.S. recommended level for fluoridation 0.7 mg/L
Canada: Health Canada MAC: 1.5 mg/L; optimal 0.7 mg/L

Where it comes from: Added by many utilities for dental health and also natural in some groundwater. Some U.S. states and cities have recently ended community fluoridation — check your utility's annual report.

Why it matters: At 0.7 mg/L it is used to prevent tooth decay. Levels well above 2 mg/L can cause dental fluorosis; very high levels over many years can affect bones.

How to reduce it: Reverse osmosis, activated alumina or distillation. Ordinary carbon pitchers do not remove much fluoride.

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U.S. limit: Not regulated for health. USGS scale: soft 0–60, moderate 61–120, hard 121–180, very hard 180+ mg/L
Canada: No guideline; 80–100 mg/L considered a good balance

Where it comes from: Water dissolving limestone, chalk and dolomite. Groundwater and western river water tend to be hardest.

Why it matters: Not harmful — calcium and magnesium are nutrients. Costs show up as scale in water heaters, dishwashers, kettles and shower glass.

How to reduce it: Ion-exchange water softener for the whole home; salt-free conditioners reduce scale but don't remove minerals. RO for drinking water if you dislike the taste.

Find a filter for Hardness (calcium & magnesium) → · Get tested for Hardness (calcium & magnesium) →

U.S. limit: Any E. coli is a violation; total coliform triggers investigation
Canada: MAC: none detectable per 100 mL

Where it comes from: Breaks in water mains, pressure loss, flooding, and for wells: septic systems, livestock or a cracked well cap.

Why it matters: Can cause acute stomach illness. Infants, older adults and immunocompromised people are most vulnerable.

How to reduce it: During a boil-water notice, bring water to a rolling boil for 1 minute (3 minutes above 6,500 ft / 2,000 m). For wells: shock chlorination plus UV disinfection certified to NSF/ANSI 55.

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U.S. limit: Uranium 30 µg/L · combined radium 5 pCi/L
Canada: Uranium MAC: 20 µg/L

Where it comes from: Natural deposits, mostly in groundwater in granite and sandstone regions.

Why it matters: Long-term exposure can affect the kidneys (uranium) and increase cancer risk (radium).

How to reduce it: Reverse osmosis or ion exchange; whole-house softeners also reduce radium.

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U.S. limit: Secondary standards: iron 0.3 mg/L, manganese 0.05 mg/L (EPA health advisory for manganese 0.3 mg/L)
Canada: Manganese MAC: 0.12 mg/L

Where it comes from: Natural in many wells; can also come from old iron mains after flushing or main breaks.

Why it matters: Iron is mostly aesthetic (rust stains, metallic taste). High manganese may affect children's neurological development.

How to reduce it: Oxidizing filters (birm, greensand), aeration or a softener for low levels; RO for drinking water.

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U.S. limit: Federal MCL 100 ppb for total chromium; California set a 10 ppb chromium-6 limit in 2024
Canada: Health Canada MAC: 50 µg/L total chromium

Where it comes from: Industrial pollution and natural deposits.

Why it matters: Considered a likely human carcinogen when ingested over long periods.

How to reduce it: Reverse osmosis or strong-base anion exchange.

Find a filter for Chromium-6 (hexavalent chromium) → · Get tested for Chromium-6 (hexavalent chromium) →

U.S. limit: No federal limit; California is the first state to require monitoring
Canada: No guideline

Where it comes from: Breakdown of plastic waste, synthetic textiles and packaging. Found in both tap and bottled water.

Why it matters: Health effects are still being studied.

How to reduce it: Carbon block filters with fine pore size and reverse osmosis remove most particles; some filters carry a specific microplastics reduction claim under NSF/ANSI 401.

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