Why Chlorine Is in Your Water — And Why You Don't Need It at Your Tap
By Sam Mendez — Chartered Process Engineer (CPEng), Engineers Australia
When people find out their tap water contains chlorine, the reaction is usually somewhere between mild concern and mild disgust. They imagine something industrial. Something that doesn’t belong in a glass of water.
The instinct isn’t wrong — but the framing usually is. Chlorine in your water is one of the most important public health interventions in history. Understanding why it’s there, and what happens to it by the time it reaches your home, changes how you think about water filtration entirely.
The Job Chlorine Was Hired to Do
Before widespread chlorination, waterborne diseases — typhoid, cholera, dysentery — were among the leading causes of death in developed cities. In the early 20th century, municipal chlorination of drinking water began in the United States, and within decades the rates of these diseases collapsed. The World Health Organisation has called water chlorination one of the most significant public health achievements of the modern era.
The mechanism is straightforward. Chlorine is a powerful disinfectant. When added to water at a treatment plant, it destroys pathogenic microorganisms — bacteria, viruses, and protozoa — that would otherwise cause serious illness. This is non-negotiable. Cities cannot distribute safe water without it.
But chlorine’s second job is equally important: residual disinfection. Water doesn’t go from treatment plant to your tap in seconds. It travels through extensive distribution networks — pipes that may be kilometres long, that pass through underground mains, street-level infrastructure, and building plumbing. During that journey, the water can pick up new microbial contamination. The residual chlorine remaining in the water continues to suppress that growth the entire way.
By the time water reaches the tap in your kitchen or the showerhead in your bathroom, the distribution system’s job is done. The residual chlorine has nothing left to protect you from.
Chloramines: The Longer-Lasting Alternative
Many Australian water utilities — particularly in Melbourne — have shifted from free chlorine to chloramines (a compound of chlorine and ammonia) as their primary residual disinfectant. Chloramines are more stable, persist longer in distribution systems, and produce fewer disinfection by-products than free chlorine.
They’re also harder to remove.
Standard activated carbon filters — the type used in most bench-top filter jugs — are highly effective at removing free chlorine but significantly less effective at removing chloramines. This is one of the reasons filter selection matters more than most consumers realise. A filter that markets itself as removing chlorine may do very little for chloramine, which is what’s actually in your water if you’re in metropolitan Melbourne, parts of Brisbane, or other urban areas.
AQVO’s shower filter reduces free chlorine (up to 98%, per supplier testing) and is less effective on chloramine — we say so on the product page. If you’re on a chloraminated supply, expect a smaller difference.
What Chlorine Does in the Shower
This is the part that surprises most people: inhalation and skin contact in a hot shower are a real exposure route — the one most people never think about.
When you step into a hot shower, two things happen simultaneously. First, your skin absorbs compounds from the water directly — your skin is in contact with warm water for several minutes. Second, heat volatilises chlorine and its by-products into the air in the enclosed shower space, and you inhale them.
Research published in environmental health literature has shown that inhalation and dermal absorption of chloroform and other trihalomethanes (disinfection by-products formed when chlorine reacts with organic matter) during showering can be significant — in some studies exceeding the contribution from drinking water.
This is why a shower filter isn’t an afterthought for health-conscious Australians. It’s arguably the more important of the two.
The By-Products Nobody Talks About
When chlorine reacts with naturally occurring organic matter in source water, it forms a family of compounds called disinfection by-products (DBPs) — most commonly trihalomethanes (THMs) and haloacetic acids (HAAs). Australian drinking water guidelines set maximum limits for these compounds, and utilities work hard to stay within them.
“Within regulated limits” means the water is safe to drink and shower in. A filter at the tap or showerhead is about the taste, smell and feel of that water, not its safety.
Point-of-use filtration at your tap and showerhead doesn’t replace a world-class treatment system. It reduces what that system was never designed to remove at the point of delivery: the residuals that have completed their job.