Water Chemistry

Chlorine and chloramine are chemical disinfectants added to municipal water supplies to eliminate harmful bacteria, viruses, and other pathogens. Chlorine has been used in water treatment 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. Both serve the same essential purpose: keeping water microbiologically safe as it travels from the treatment plant to your home.

These disinfectants are present in tap water because federal regulations require municipal systems to maintain a residual disinfectant level throughout the distribution network. This ensures protection against microbial contamination even in pipes far from the treatment facility. The EPA sets maximum residual disinfectant levels (MRDLs) at 4 mg/L for chlorine and 4 mg/L for chloramine. Most utilities operate well within these limits. While disinfection is essential for public health, some people notice a taste or odor associated with chlorine, particularly when levels are at the higher end of normal ranges.

Standard water testing can measure both free chlorine and total chlorine (which includes chloramine). Results typically show concentrations in milligrams per liter. Testing at the tap can be informative because disinfectant levels 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 (DBPs) are chemical compounds that form when disinfectants like chlorine react with naturally occurring organic matter in the water supply. The two most commonly measured groups are trihalomethanes (THMs) and haloacetic acids (HAAs). These are not added to water intentionally -- they are unintended consequences of the disinfection process itself, which creates a balancing act between eliminating pathogens and minimizing byproduct formation.

THMs and HAAs are present because organic matter from soil, decaying vegetation, and agricultural runoff naturally enters source water. When chlorine or chloramine interacts with this organic material, DBPs form. Their concentration can vary seasonally, often increasing in warmer months when organic matter levels in source water rise. The EPA regulates total trihalomethanes (TTHMs) with a maximum contaminant level (MCL) of 80 parts per billion (ppb) and total haloacetic acids (HAA5) at 60 ppb. Utilities monitor these levels routinely and report results in annual Consumer Confidence Reports.

Laboratory water testing can detect specific THMs and HAAs and measure their concentrations against EPA standards. Because DBP levels can fluctuate based on season, source water conditions, and distance from the treatment plant, point-of-use testing provides a snapshot of what is actually present at your tap at a given time. This information can be useful context alongside your utility's system-wide monitoring data.

Metals in household water come from a variety of sources. Lead and copper most commonly enter water through contact with plumbing materials -- lead service lines, older solder joints, and copper piping can all contribute. Iron and manganese, on the other hand, are typically present in source water due to natural geological deposits. Each of these metals behaves differently in water and is associated with distinct characteristics. Lead is colorless and tasteless. Copper can produce a metallic taste and blue-green staining. Iron often causes reddish-brown discoloration, while manganese tends to create dark brown or black staining.

The EPA regulates lead and copper under the Lead and Copper Rule (LCR), which sets an action level of 15 ppb for lead and 1.3 mg/L for copper at the tap. These are not maximum contaminant levels but rather triggers for additional treatment or corrective measures by the utility. Importantly, the EPA states that there is no safe level of lead exposure, which is why even low levels warrant awareness. Iron and manganese are regulated as secondary contaminants with recommended limits of 0.3 mg/L and 0.05 mg/L respectively -- these are based on aesthetic concerns like taste, odor, and staining rather than health effects at typical concentrations.

Water testing for metals is particularly informative because levels can vary significantly from home to home depending on plumbing age, materials, and water chemistry. A first-draw sample -- collected from water that has been sitting in pipes for several hours -- is the standard method for measuring lead and copper at the tap. This approach captures the highest likely concentration from contact with household plumbing.

Water hardness refers to the concentration of dissolved calcium and magnesium minerals. As water moves through limestone, chalk, and other geological formations, it naturally absorbs these minerals. Hardness is one of the most common water quality characteristics and varies significantly by region. Water is generally classified as soft (0-60 mg/L), moderately hard (61-120 mg/L), hard (121-180 mg/L), or very hard (above 180 mg/L), measured as calcium carbonate equivalents.

Calcium and magnesium are present in water because of the geology of the source watershed. Regions with limestone or dolomite bedrock tend to have harder water. Hardness is not regulated by the EPA as a health concern -- in fact, these minerals are nutritionally essential. However, hard water is associated with practical household effects: scale buildup on fixtures and inside water heaters, reduced soap lathering, spots on glassware, and over time, decreased efficiency in water-using appliances. These are quality- of-life and maintenance considerations rather than health issues.

Testing for hardness is straightforward and commonly included in basic water analyses. Results are reported in milligrams per liter (mg/L) or grains per gallon (gpg). Understanding your water's hardness level provides useful context for decisions about household maintenance, appliance care, and whether water conditioning might be beneficial for your specific situation.

Sediment in household water refers to small suspended particles that can include sand, silt, clay, rust flakes, and other particulate matter. These particles can give water a cloudy or discolored appearance and may occasionally be visible as small specks. Sediment is one of the most noticeable water quality issues because it directly affects the look and sometimes the feel of water coming from the tap.

Sediment can originate from several sources. Naturally occurring particles may enter the water supply from the source watershed, particularly after heavy rains or seasonal changes. More commonly, sediment in household water comes from aging distribution infrastructure -- corroding iron mains, disturbed pipe scale, or construction activity on water lines. Within the home, older galvanized steel pipes are a frequent contributor of rust particles. The EPA regulates turbidity (a measure of water clarity related to suspended particles) as part of surface water treatment requirements, but sediment at the tap often reflects conditions in the distribution system or household plumbing rather than treatment plant performance.

Water testing can measure turbidity in nephelometric turbidity units (NTU) and identify the composition of particulate matter. Sudden changes in sediment levels -- such as after a water main break, hydrant flushing, or plumbing work -- are common and usually temporary. Persistent sediment may indicate aging infrastructure that warrants further investigation.

PFAS are a large family of synthetic chemicals that have been manufactured and used in a wide range of industrial and consumer products since the 1940s. Often called "forever chemicals" because of their persistent molecular structure, PFAS are found in nonstick cookware, water-resistant fabrics, food packaging, firefighting foams, and many other applications. Their chemical stability -- the same property that makes them useful in products -- also means they do not break down easily in the environment, and they have been detected in water supplies, soil, and even blood samples across the population.

PFAS can enter water supplies through industrial discharge, wastewater treatment outflows, landfill leachate, and the use of PFAS-containing firefighting foams, particularly near military bases and airports. The science around PFAS health effects is evolving, and regulatory agencies are actively updating their guidance. In 2024, the EPA finalized the first-ever national drinking water standard for six PFAS compounds, setting maximum contaminant levels at 4 parts per trillion (ppt) for PFOA and PFOS individually, with limits for other PFAS compounds as well. Utilities are in the process of monitoring and, where necessary, implementing treatment to meet these standards. It is worth noting that detection of PFAS in water does not automatically indicate a health concern -- context including concentration levels and specific compounds matters.

Specialized laboratory testing can detect PFAS at extremely low concentrations using methods such as EPA Method 533 and EPA Method 537.1. Standard home test kits typically do not test for PFAS, so laboratory analysis is recommended for anyone seeking this specific information. Many utilities are now including PFAS monitoring data in their public reporting, which provides another useful reference point for understanding what may be present in your local supply.

Microplastics are tiny plastic fragments, typically smaller than 5 millimeters, that originate from the breakdown of larger plastic products, synthetic textiles, industrial processes, and personal care products containing microbeads. Research over the past decade has documented their widespread presence in oceans, rivers, soil, and the atmosphere. More recently, studies have detected microplastics in both bottled and tap water, making them a subject of growing scientific interest.

Microplastics are present in water for several reasons. They enter waterways through stormwater runoff, wastewater treatment plant effluent, and atmospheric deposition. Conventional water treatment processes were not specifically designed to remove particles of this type, although some treatment steps do reduce their presence. Currently, there are no federal drinking water standards for microplastics in the United States, and the research on potential health effects from ingestion through drinking water is still in relatively early stages. The World Health Organization published a review in 2019 concluding that microplastics in drinking water do not appear to pose a health risk at current levels, while recommending continued research.

Testing for microplastics in drinking water requires specialized laboratory analysis and is not yet part of standard water quality panels. As analytical methods improve and research advances, monitoring capabilities are expected to become more accessible. For now, microplastics represent an area of active scientific inquiry where understanding is still developing.

Nitrates are naturally occurring inorganic compounds composed of nitrogen and oxygen. In small amounts, they are a normal part of the nitrogen cycle and are found in soil, water, and many foods -- particularly leafy green vegetables. In the context of drinking water, nitrates become a topic of interest when concentrations exceed background levels, which can happen due to human activity affecting groundwater and surface water sources.

Elevated nitrate levels in water most commonly result from agricultural fertilizer runoff, animal waste, septic system leachate, and wastewater discharge. Rural and agricultural communities that rely on well water are particularly likely to encounter higher nitrate concentrations. The EPA sets a maximum contaminant level of 10 mg/L for nitrate (measured as nitrogen) in public water supplies. This standard is specifically protective of infants, as high nitrate levels can interfere with the blood's ability to carry oxygen in very young children -- a condition known as methemoglobinemia or "blue baby syndrome." For most adults, nitrate levels at or below the MCL are not considered a health concern.

Nitrate testing is commonly included in standard water quality panels and is straightforward to perform. For households using private wells, periodic nitrate testing is recommended by the EPA and state health departments, particularly in agricultural areas. Municipal systems monitor nitrate levels routinely and report results in annual water quality reports.

Volatile organic compounds (VOCs) are a broad category of carbon-based chemicals that easily evaporate at room temperature. Common examples include benzene, toluene, trichloroethylene (TCE), and perchloroethylene (PCE). These compounds are widely used in industrial solvents, fuels, degreasers, dry cleaning chemicals, and various manufacturing processes. In the context of drinking water, VOCs are of interest because some of them have been associated with health effects at elevated concentrations over extended periods of exposure.

VOCs enter water supplies primarily through industrial discharge, improper chemical disposal, underground storage tank leaks, and contaminated groundwater plumes. Because they evaporate readily, VOCs are more commonly a concern in groundwater-sourced systems than in surface water supplies. The EPA regulates numerous individual VOCs under the Safe Drinking Water Act, each with its own maximum contaminant level. For example, the MCL for benzene is 5 ppb, for TCE it is 5 ppb, and for PCE it is 5 ppb. Public water utilities are required to monitor for regulated VOCs and treat water that exceeds these standards.

VOC testing requires laboratory analysis, as these compounds are typically present at very low concentrations measured in parts per billion. Comprehensive VOC panels can screen for dozens of individual compounds simultaneously. For homes served by municipal water, utilities handle VOC monitoring as part of their regulatory obligations. For private well owners, VOC testing is advisable if the well is located near industrial sites, gas stations, dry cleaners, or known contamination zones.