Nanobubbles vs Chlorine: An Honest Comparison

In short

Chlorine works by putting a reactive chemical into the water and keeping it there. Nanobubbles work by putting an enormous amount of gas-to-water surface through the treatment loop and letting oxidation happen there. Almost every other difference between the two follows from that one structural fact.

A chlorinated pool carries measurable disinfectant at every point in the basin. That is exactly what makes it so hard to beat on safety, and exactly what produces the smell, the stinging eyes and the disinfection by-products. A nanobubble pool treats water as it passes the plant, forms no chloramines of its own, and leaves no chemical residue for bathers to react to.

• Chlorine is better at holding a residual across the whole basin, shock dosing after an incident, low capital cost, and being serviceable by any pool technician in the country.
• Nanobubbles are better at stopping chloramines and disinfection by-products at source, cutting chemical purchasing, improving clarity, and taking corrosive load off the building.
• Most facilities land in between: nanobubbles carry the disinfection work, and a small chlorine residual is kept because the regulation asks for it.

If you want the wider picture — active oxygen, salt and UV as well — start with chlorine-free pools — full guide.

How chlorine works

Whatever form you buy it in — hypochlorite solution, granules, tablets, or salt run through an electrolysis cell — pool chlorine ends up in the water as hypochlorous acid. It is a small, uncharged, highly reactive molecule that passes through microbial cell walls and destroys the machinery inside. It is genuinely excellent at that job, which is why it has not been displaced in a century.

Two consequences follow from the chemistry. First, hypochlorous acid stays dissolved in the water, so a correctly dosed pool has disinfectant present everywhere, not only in the plant room. That is residual disinfection, and it is chlorine’s real advantage. Second, hypochlorous acid reacts with everything else in the water too — and that is where the trouble starts.

pH control decides how much of your dosed chlorine is actually present as hypochlorous acid rather than the far weaker hypochlorite ion. Above roughly pH 7.6, a large share of your free chlorine is doing very little work. A great many “we need more chlorine” problems are really pH problems, and no alternative technology removes the need to manage water balance.

Chloramines, trihalomethanes and the rest of the by-products

Most of what gets filed under the dangers of chlorine in swimming pools is not caused by chlorine itself. It is caused by what chlorine makes when it meets what swimmers bring into the water.

• Chloramines — combined chlorine — form when free chlorine reacts with ammonia and nitrogen compounds from sweat, urine, skin cells and cosmetics. Trichloramine is volatile: it leaves the water, collects above the surface, and is what you actually smell and breathe in an indoor hall.
• Trihalomethanes form when chlorine reacts with dissolved organic carbon. They are the most studied group of disinfection by-products in pool water and the reason bather hygiene rules — shower before swimming — exist at all.
• Both scale with organic load rather than with how carefully the plant is run. Reduce the organic load, or reduce the chlorine, and both fall.

None of this makes a well-run chlorinated pool unsafe. It does mean chlorine comes with an unavoidable trade: the molecule that protects bathers is the same molecule that produces the irritation, the smell and the corrosion. You cannot keep one and discard the other.

How nanobubbles work

Nanobubbles are gas-filled bubbles smaller than roughly 200 nanometres across. At that scale buoyancy barely acts on them, so they do not rise and burst the way aeration bubbles do. They stay suspended for days, carry a strong negative surface charge, and pack an enormous combined gas-liquid surface area into an ordinary volume of water.

The NanoSWIM Pool System sits in the circulation loop after filtration and generates those bubbles continuously, charged with oxygen or with ozone. Three things then happen.

1. Gas transfer. The surface area is the whole point. Coarse injection loses most of its gas at the water surface before it has dissolved; nanobubbles transfer far more of it into solution, which is why the same ozone generator does more work behind a nanobubble system than behind a venturi.
2. Oxidation. Individual bubbles collapse and release concentrated oxidative energy at microscopic scale. That disrupts pathogen cell membranes and breaks down the organic precursors that would otherwise have become chloramines.
3. Surface effects. The negative charge lifts fine particles and biofilm off walls, ladders and pipework so the filter can capture them. Operators usually notice the water looks different before any test result confirms it.

The underlying physics is set out on how nanobubbles work. The point that matters for a chlorine vs nanobubble decision is where the work happens: nanobubble treatment acts on water passing through the plant and on the bubbles that travel back out with it. It is not a chemical residual, and we will not pretend it is one.

Dimension	Chlorine	NanoSWIM nanobubbles
Disinfection mechanism	Hypochlorous acid dissolved throughout the water, oxidising continuously	Oxidation from bubble collapse plus dissolved oxygen or ozone, concentrated in the treatment loop
Residual in the basin	Yes — measurable free chlorine at every point	None on its own; a small chlorine residual is normally retained where the regulation requires it
By-products	Chloramines and trihalomethanes form in proportion to bather load	No chloramines formed; ozone reverts to oxygen and leaves nothing behind
Existing chloramines	Removed only by breakpoint chlorination or a secondary system	Precursors are oxidised, so new combined chlorine stops forming
Operating cost	Lowest cost per cubic metre today; tracks chemical prices upward	A steady, modest energy draw; chemical spend falls sharply
Maintenance and consumables	Dosing pumps, probes, calibration, deliveries and chemical storage	Scheduled servicing of the generator; no drums to store, handle or transport
Capital cost	Low — dosing equipment is inexpensive	Higher — this is a plant purchase, not a consumable
Regulatory position	The assumed default in Norwegian bathing-facility rules	Used as primary treatment with a reduced residual; agreed with the municipal health authority
Bather experience	Chlorine smell, eye irritation and tight skin once combined chlorine climbs	No chlorine smell, no stinging eyes, noticeably softer on skin
Best fit	Small, seasonal or tightly budgeted pools; anywhere a full residual is mandatory and cheap to hold	Indoor halls, heavy bather loads, hotels, therapy and swim-school pools where air quality and chemical spend cost real money

Operating cost is indicative. It moves with bather load, water temperature, local energy and chemical prices, and how the plant is actually run. Ask any supplier — including us — for figures against your pool volume and turnover rate rather than a generic table.

Where chlorine is still better

This is the section most supplier websites leave out. These are the places where a chlorine-dosed pool is the better engineering answer, stated without a qualifier attached.

• It holds a residual everywhere. A swimmer who introduces contamination at the far end of a 25-metre pool is dealt with immediately, long before that water reaches the plant room. No treatment-loop technology — not nanobubbles, not UV, not ozone — can do that. It is the single strongest argument for chlorine, and it is why regulators are attached to it.
• You can shock the pool. After a faecal accident, a norovirus incident or an algae bloom, chlorine gives you a fast, high-dose response with published contact times and a documented procedure. There is no equivalent emergency lever on a nanobubble system, and a facility that needs one should keep chlorine available.
• It is cheap to buy and cheap to install. Two dosing pumps, a probe and a tank cost a fraction of any equipment-based alternative. For a small outdoor pool that opens twelve weeks a year, the payback period on anything else is effectively never.
• Anyone can service it. Parts are on the shelf, the failure modes are understood, and you are not tied to one supplier for fifteen years. On a plant that has to keep running through staff changes and budget freezes, that independence has genuine value.
• It is trivially measurable. A colour test kit costs almost nothing and produces a number an inspector accepts on the spot. Documenting disinfection performance on any alternative takes more effort, and you should budget for that effort rather than discover it.
• It is the regulatory default. Norwegian bathing-facility rules are written around a measurable residual. Anything else has to be discussed and documented with the municipal health authority rather than simply installed.

If most of that list describes your pool, buy chlorine. We would rather tell you now than after a site visit.

Where nanobubbles win

The case for a chlorine alternative is strongest wherever the by-products, not the disinfection, are what cost you money.

• Indoor air quality. No chlorine dosed means no chloramines formed, which means no trichloramine collecting above the water. For a swim school, a therapy pool or a hotel with a basement pool hall, this is usually the whole business case on its own.
• Chemical purchasing. Reducing chemical use substantially against a conventional dosing regime changes a budget line permanently, and chemical prices have only moved in one direction. One resort pool documented an 85% reduction in chlorine after switching — the working is in the resort pool case study.
• Bathers with sensitive skin or airways. People with eczema, chlorine rash or asthma are the group that notices the difference first, and they are also the group most likely to stop coming to a pool that irritates them.
• Clarity and biofilm. Fine particulate and biofilm come off surfaces and into the filter. Cleaner surfaces also mean less disinfectant demand, which compounds the chemical saving.
• The building itself. Chloramines are corrosive to ductwork, fixings, handrails and ceiling structures. That damage is slow, expensive and rarely attributed to the pool chemistry that caused it.

Cost over five years

There is no honest single number here, because a municipal 25-metre pool and a hotel plunge pool are not the same purchase. What is predictable is the shape of the operating cost, and that is what you should be comparing.

• Year zero. Chlorine wins outright. Dosing equipment is cheap and installation is quick. A nanobubble system is a plant purchase and it shows up in the capital budget.
• Chemicals. This is where the money comes back, and it comes back every year. Ask for your current annual chemical spend and model the reduction against it rather than against a supplier’s average.
• Energy. Modest and continuous. Ask every supplier for kW draw at your flow rate, then multiply by your own tariff — not theirs.
• Consumables and labour. Chlorine plants consume probes, calibration solution and staff time on dosing and testing. Ask what wears out on any alternative, how often, and what a replacement costs.
• Ventilation and building maintenance. Real, significant and hard to invoice. Treat it as upside rather than as the core of the case, and it will not embarrass you in a budget meeting.

A useful discipline when comparing quotes: ask for a five-year total on your actual pool volume, including consumables, energy and servicing. A supplier who cannot produce that is quoting a box rather than a solution.

What the regulations say about residual disinfection

Public pools in Norway operate under the bathing-facility regulation (forskrift om badeanlegg, bassengbad og badstu), enforced by the municipal health authority. It sets requirements for water quality and monitoring rather than prescribing one technology, but the practical effect is consistent.

• A public pool is normally expected to maintain a measurable disinfectant residual in the basin, so that contamination introduced by one bather cannot reach another before the water has been circulated and treated.
• That makes a zero-chlorine public pool rare. The realistic outcome is a heavily reduced chlorine level, with nanobubbles carrying the disinfection load and a small residual kept for compliance.
• Private pools, hotel pools and spas are treated differently and have far more freedom to run genuinely chlorine-free.
• Documentation is what municipal buyers actually ask about: which standards a system meets, how performance is measured, and how results are logged.

We keep the compliance detail — what a public buyer will ask for and what any supplier should be able to hand over — on the page covering residual disinfection requirements.

Who should choose what

A short routing guide, written to send some readers away from us.

Stay on conventional chlorine if

• Your pool is small, seasonal, outdoors, or lightly used, and the chemical bill is not a meaningful line in your budget.
• You have no indoor air-quality complaints and no corrosion problem.
• Capital is unavailable and operating budget is not the constraint.
• You need the ability to shock-dose frequently because of the bather profile you serve.

Add nanobubbles alongside a reduced chlorine residual if

• You run an indoor hall and air quality, complaints or staff comfort are a recurring issue.
• You are a public facility that must keep a residual but wants to cut chemical use and combined chlorine hard.
• Your ventilation plant or building fabric is showing chloramine-driven wear.

Go as close to chlorine-free as your regulator allows if

• You operate a hotel, spa, therapy or private pool where the bather experience is part of what you sell.
• A significant share of your users have sensitive skin, eczema or asthma.
• You are building new and can specify the plant properly rather than retrofit around it.

Considering a salt system instead? A salt chlorinator is still a chlorine system — see Nanobubbles vs salt. If you already have UV or ozone, Nanobubbles vs UV and Nanobubbles vs ozone cover how those combine with nanobubble treatment.