Water Chemistry
A clear look at the substances that can be present in household water — what they are, why they're there, and what testing reveals.
Water Chemistry Overview Guide
A comprehensive reference guide covering the key substances found in household water and what they mean.
Water is rarely "just water." By the time it reaches your faucet, it has traveled through watersheds, treatment facilities, and miles of distribution infrastructure. Along the way, it picks up substances -- some added intentionally, some occurring naturally, and some introduced by the materials it contacts.
This page provides a straightforward overview of the most commonly discussed substances found in household water. For each one, we cover what it is, why it may be present, what regulatory standards address, and what water testing can reveal. The goal is not to alarm, but to inform.
Chlorine & Chloramine
Chlorine and chloramine are chemical disinfectants added to municipal water supplies to eliminate harmful bacteria, viruses, and other pathogens. Chlorine has been used since the early 1900s and is widely credited with dramatically reducing waterborne diseases. Chloramine — a compound formed by combining chlorine with ammonia — is increasingly used as a longer-lasting alternative.
Federal regulations require municipal systems to maintain a residual disinfectant level throughout the distribution network. The EPA sets maximum residual disinfectant levels (MRDLs) at 4 mg/L for both chlorine and chloramine. Most utilities operate well within these limits, though some people notice a taste or odor at higher concentrations.
Standard water testing can measure both free chlorine and total chlorine. Results at the tap can vary depending on your distance from the treatment facility, the time of year, and the age of the distribution infrastructure in your area.
Disinfection Byproducts (THMs & HAAs)
Disinfection byproducts form when chlorine reacts with naturally occurring organic matter in source water. The two most commonly measured groups are trihalomethanes (THMs) and haloacetic acids (HAAs). They are not added intentionally — they are unintended consequences of the disinfection process, creating a balancing act between pathogen elimination and byproduct formation.
The EPA regulates total trihalomethanes (TTHMs) with a maximum contaminant level of 80 ppb and total haloacetic acids (HAA5) at 60 ppb. Concentrations can fluctuate seasonally, often increasing in warmer months when organic matter in source water rises. Laboratory testing can detect specific THMs and HAAs and measure them against these federal limits.
Lead, Copper, Iron & Manganese
Metals enter household water from multiple sources. Lead and copper most commonly leach from plumbing materials — lead service lines, older solder joints, and copper piping. Iron and manganese are typically present due to natural geological deposits in the source water. Each behaves differently: lead is colorless and tasteless, copper can produce metallic taste and blue-green staining, iron causes reddish-brown discoloration, and manganese creates dark brown or black staining.
The EPA's Lead and Copper Rule sets an action level of 15 ppb for lead and 1.3 mg/L for copper at the tap. The EPA states there is no safe level of lead exposure. Iron and manganese are regulated as secondary contaminants at 0.3 mg/L and 0.05 mg/L respectively, based on aesthetic concerns rather than health effects.
A first-draw sample — collected after water has been sitting in pipes for several hours — is the standard method for measuring lead and copper, capturing the highest likely concentration from household plumbing contact.
Additional Substances in Household Water
Water hardness refers to dissolved calcium and magnesium minerals absorbed as water moves through limestone and other geological formations. Classified from soft (0–60 mg/L) to very hard (above 180 mg/L), hardness causes scale buildup, reduced soap lathering, and decreased appliance efficiency. It is not regulated by the EPA as a health concern since these minerals are nutritionally essential, but testing provides useful context for household maintenance decisions.
Sediment includes suspended particles such as sand, silt, clay, and rust flakes that can make water cloudy or discolored. It most commonly originates from aging distribution infrastructure, corroding iron mains, or older galvanized steel household pipes. The EPA regulates turbidity as part of surface water treatment requirements, though sediment at the tap often reflects distribution system or household plumbing conditions rather than treatment plant performance.
PFAS are synthetic “forever chemicals” used since the 1940s in nonstick cookware, water-resistant fabrics, and firefighting foams. They enter water supplies through industrial discharge, landfill leachate, and contaminated runoff. In 2024, the EPA finalized the first national drinking water standard for six PFAS compounds, setting MCLs at 4 parts per trillion for PFOA and PFOS. Specialized laboratory methods (EPA 533 and 537.1) are required for detection, as standard home test kits do not cover PFAS.
Microplastics are tiny plastic fragments smaller than 5 millimeters originating from the breakdown of larger plastics, synthetic textiles, and personal care products. They enter waterways through stormwater runoff and wastewater effluent, and conventional treatment was not designed to remove them. There are currently no federal drinking water standards for microplastics, and the WHO has concluded they do not appear to pose a health risk at current levels, though research is ongoing.
Nitrates are inorganic compounds that enter water primarily through agricultural fertilizer runoff, animal waste, and septic system leachate. Rural communities on well water are most likely to encounter elevated levels. The EPA sets an MCL of 10 mg/L (as nitrogen), a standard specifically protective of infants since high nitrate levels can cause methemoglobinemia (“blue baby syndrome”). Periodic testing is recommended for private well owners, particularly in agricultural areas.
VOCs are carbon-based chemicals — including benzene, trichloroethylene (TCE), and perchloroethylene (PCE) — that evaporate easily and enter water supplies through industrial discharge, underground storage tank leaks, and contaminated groundwater plumes. The EPA regulates numerous individual VOCs, each with its own MCL (for example, 5 ppb for benzene, TCE, and PCE). Laboratory analysis is required for detection, and VOC testing is especially advisable for private wells near industrial sites or known contamination zones.
What Testing Reveals
Point-of-Use vs. System Testing
Utility monitoring captures system-wide averages, but conditions at your tap can differ based on household plumbing age, materials, and local distribution infrastructure. Point-of-use testing provides a snapshot of what you actually consume.
First-Draw Sampling
Collecting water that has sat in pipes for 6+ hours captures peak concentrations of lead, copper, and other metals that leach from plumbing. This EPA-recommended method reveals exposure levels that flushed-line samples would miss.
Specialized PFAS Analysis
Standard test panels do not include PFAS. Detecting these compounds at parts-per-trillion levels requires EPA Method 533 or 537.1 laboratory analysis — the only reliable way to measure whether your water meets the new 4 ppt federal standards.
Get a Clear Reading of Your Water
Understanding water chemistry starts with knowing what's actually in yours.