Many utilities have switched from plain chlorine to chloramine because it lasts longer on the way from the treatment plant to your tap. It still disinfects effectively, but it can leave a stronger chemical taste or smell, and it's a bit harder to filter out than chlorine alone.

Most municipal utilities add a small, carefully controlled amount of fluoride to help prevent tooth decay — a practice that's been standard since the 1950s. It's considered safe at typical levels, though some households still choose to filter it out.

The most widely used disinfectant in U.S. drinking water, chlorine is added at the treatment plant to kill bacteria and other pathogens before water ever reaches your home. It does its job well — it's also usually the reason tap water sometimes has a faint pool-like smell.

Disinfection byproducts form when chlorine or chloramine reacts with organic material already present in the source water. Fairfax Water routinely reports both TTHMs and HAA5 in its treated water, staying within EPA limits — a reminder that "disinfected" doesn't mean nothing else is there.

Hardness comes from calcium and magnesium naturally present in the source water, not from anything added or gone wrong. Arlington's water runs around 142 mg/L — about 8 grains per gallon, moderately hard — enough to leave spots on glassware and scale buildup in pipes and appliances over time.

Lead rarely comes from the water itself — it's usually picked up from aging service lines, old solder, or fixtures on the way to your tap. Beyond the health concerns, including developmental effects in children and elevated blood pressure in adults, it's also a common cause of staining on dishes, laundry, and plumbing fixtures.

PFAS are synthetic "forever chemicals" that have been used for decades in nonstick cookware, water-resistant fabric, and firefighting foam — and they don't break down naturally in the environment or the body. They're linked to a range of health concerns and are notoriously difficult to remove with standard water treatment.

Rust and iron particles can give water a metallic taste and a reddish or brownish tint, along with staining on clothes, dishes, and fixtures. At high enough levels, they can also clog pipes and shorten the life of appliances.

Nitrate and nitrite typically enter water through fertilizer runoff or septic systems, and can cause gastrointestinal illness at elevated levels. They're a particular concern for infants and pregnant women, which is why they're one of the first things worth testing for on a private well.

Water with a low pH is naturally corrosive. Over time it can eat away at copper pipes, appliances, and fixtures, leave blue-green stains around drains, and give water a sour or metallic taste. The bigger concern is that corrosion can pull metals like lead and copper into the water you drink.

Radon is a naturally occurring radioactive gas that can dissolve into well water from the surrounding bedrock. It has no taste, smell, or color, so testing is the only way to know it's there. The main risk comes when it's released into your indoor air during showers and everyday water use, and long-term exposure is linked to lung cancer.

Bacteria such as E. coli, along with viruses and parasites like giardia, can get into water through a cracked well casing, flooding, or a failing septic system. They can cause stomach illness and, in some cases, serious infection. Since you can't see, smell, or taste them, regular testing is the only reliable check, especially for private wells.