Swimming Pool Water Treatment — Without Chlorine Smell or Stinging Eyes

What a swimming pool demands from its water treatment

Pool water is a harder problem than most water because the contamination arrives on a schedule you do not control. A school group at eleven and an empty hall at three are the same pool with completely different organic loads, and the treatment has to cope with both without anyone touching a dial.

Whatever technology sits in the plant room, four jobs have to be covered:

• Circulation and turnover. Every litre in the basin has to reach the plant room often enough. Turnover rate is the number that governs everything else, and it is the first thing any supplier should ask you for.
• Filtration. Physical removal of everything that can be filtered. No disinfection method replaces a working filter — nanobubbles included.
• Pool disinfection. Inactivating what filtration cannot catch, fast enough to matter between one bather and the next.
• Oxidation. Breaking down the dissolved organic material — sweat, urine, skin oils, cosmetics, sunscreen — that filtration leaves behind. This is where most of the chemical goes, and it is the job nanobubbles are best at.

The air in the hall is part of the water problem

In an indoor facility, pool water quality and hall air quality are the same conversation. Free chlorine reacting with organic load produces chloramines, which leave the water and sit in the air above it. That is the sharp chlorine smell people associate with a clean pool, and it is exactly backwards: a well-run pool smells of almost nothing.

Chloramines are what your ventilation plant is really fighting, what corrodes ladders, handrails, grouting and ductwork, and what instructors and lifeguards breathe for eight hours a day. Remove the source and the ventilation problem shrinks with it. If you are weighing the options generally rather than for one pool, the chlorine-free pool guide compares all five methods side by side.

How nanobubbles replace chlorine in the treatment loop

Nanobubbles are gas-filled bubbles below roughly 200 nanometres across. At that size buoyancy barely acts on them, so instead of rising and bursting they stay suspended for days, carrying a negative surface charge and an enormous combined surface area. A NanoSWIM generator sits in the existing circulation loop, after filtration, and the water passing through it does four things:

1. Generation. The unit produces nanobubbles of oxygen or ozone at high density in the passing flow.
2. Gas transfer. Because the combined surface area is so large, far more gas actually dissolves than with coarse injection, where most of it escapes at the surface before transferring anything.
3. Oxidation. Individual bubbles collapse and release concentrated oxidative energy at microscopic scale, disrupting pathogen cell membranes and breaking down the organic compounds that would otherwise have become chloramines.
4. Clarity. The negative surface charge lifts fine particles and biofilm off basin walls, tiles and pipework so the filter can take them out. This is why crystal clear pool water usually shows up before the first set of test results does.

The honest limit is the same one that applies to UV and ozone: this is a treatment-loop technology. It acts on water passing through the system and leaves no lasting residual in the basin on its own, which is exactly why a public facility normally keeps a small chlorine residual alongside it. The detailed head-to-head is on Nanobubbles vs chlorine, and if you are currently costing up a lamp bank or a salt cell instead, see Nanobubbles vs UV and Nanobubbles vs salt chlorinators.

Which system suits which pool

The NanoSWIM Pool System is the standard unit for pools and aquatic facilities, built in SS 304 and rated for flow up to 500 m³/h. NanoSWIM Pro is the commercial version in SS 316L, rated to 800 m³/h and specified where bather loads are heavy and sustained. The Compact Unit covers small installations at up to 60 m³/h where plant-room space is the constraint.

Sizing follows your flow rate and turnover, not your basin length. Send both figures and the answer is usually obvious within a day.

Before and after: what a pool operator actually sees change

The table below is deliberately written in terms of what an operator watches week to week rather than in percentages we cannot stand behind for your pool. Two numbers are ours to publish: chemical use falls by up to 90% against conventional dosing on comparable pools, and one documented resort installation cut chlorine by 85%. Everything else in this table is a direction of travel, not a promise.

What you watch	Conventional chlorine dosing	With nanobubble treatment
Chemical spend	The largest recurring consumable line, and it moves with the chemical market	Falls substantially — up to 90% less against conventional dosing; 85% at the documented resort pool
Combined chlorine	Forms continuously wherever free chlorine meets sweat, urine and sunscreen	Nothing dosed means nothing left for chloramines to form from
Air in the hall	The familiar chlorine smell; ventilation runs hard to keep it tolerable	The smell goes as combined chlorine falls, and the ventilation load falls with it
Water clarity	Good with a well-maintained filter, but fine particles and biofilm keep coming back	Particles and biofilm lift off surfaces for the filter to catch; usually the first change staff notice
Bather comfort	Stinging eyes, dry skin, chlorine rash, and complaints from the regulars	No chemical residue for skin, eyes or airways to react to
Building and fixtures	Corrosive load on ladders, handrails, grouting, fittings and ductwork	That load largely disappears; wear returns to ordinary building rates
Energy	Dosing pumps cost almost nothing to run; dehumidification and ventilation do not	The generator draws power continuously, offset against a lower hall ventilation demand
Monitoring and logging	Free chlorine, combined chlorine, pH and water balance	Still required, and no less often — a different set of parameters, not fewer of them

Nothing here is a guarantee for your facility. Bather load, water temperature, turnover rate, filter condition and how the plant is operated all move these outcomes. Ask us — and every other supplier — for figures worked against your own volume and turnover.

Pool water quality and the rules that apply in Norway

Public pools in Norway operate under the bathing-facility regulations (forskrift om badeanlegg, bassengbad og badstu), enforced by the municipal health authority, with supporting guidance from the Norwegian Institute of Public Health. The regulation sets requirements for water quality, monitoring and documentation rather than prescribing a particular technology, which has three practical consequences:

• A public pool normally has to keep a measurable disinfectant residual in the basin, so contamination from one bather cannot reach another before the water has circulated. A genuinely zero-chlorine public pool is therefore rare.
• What a public facility can realistically reach is a heavily reduced chlorine level, with nanobubbles carrying the oxidation and disinfection load. That is enough for the smell and the eye irritation to go.
• Private pools, hotel pools, spas and therapy pools are treated differently and have far more room to run fully chlorine-free.
• Documentation is what municipal buyers actually scrutinise: which parameters are logged, how often, by whom, and what happens when a reading falls outside range.

If you are specifying a municipal facility, the public aquatic facilities page is written around that procurement process rather than around the technology.

Suitable for: private, hotel, public and therapy pools

The same physics applies everywhere, but the reason for buying differs enough that it is worth being explicit.

• Private pools. The most straightforward case. No residual requirement, low and predictable load, and fully chlorine-free operation is realistic. The usual driver is a family member who reacts badly to chlorine.
• Hotel and spa pools. Guest experience is the business case, and it is a strong one: no chlorine smell in the corridor outside the spa, and no dry skin after a swim. Pool sanitation still has to hold up under unpredictable occupancy. See solutions for hotels and spa.
• Public and municipal facilities. The largest chemical budgets, the heaviest bather loads and the strictest documentation. Expect reduced chlorine rather than none, and expect the air-quality improvement to matter as much to the staff as to the swimmers.
• Therapy and rehabilitation pools. Warm water, long dwell times and users with sensitive skin or airways — the group that reacts most to chloramines and notices the change first.
• Where it fits less well. Outdoor pools with no enclosure lose the air-quality half of the argument, and a small, lightly used pool with an already modest chemical bill may not pay the capital cost back on chemicals alone. We will say so.

Annual operating cost, and how to work out yours

There is no honest single figure, because a 25-metre municipal pool and a hotel plunge pool are not the same purchase. What is predictable is the shape of the annual cost, and you can build your own estimate from lines you already have in front of you.

1. Start with your chemical invoices. Take twelve months of actual spend on chlorine and pH correction. This is the line that moves most, and it is the one you can verify yourself afterwards.
2. Add energy. Ask for the kW draw of the unit at your flow rate, run it against your own tariff and your own operating hours. Do not accept a generic annual figure.
3. Subtract ventilation and dehumidification load. Harder to quantify precisely, but in an indoor hall it is real money once combined chlorine drops.
4. Add consumables and service. Ask what wears out, on what interval and at what price. A system with no consumables should be able to say so plainly.
5. Look at five years, not one. Capital cost divided over a realistic life, plus running cost, against your current total. Any supplier who cannot produce that table is quoting a box rather than a solution.

Two costs are usually left out of comparisons and should not be: the staff hours spent handling and dosing chemicals, and the slow replacement cost of fixtures and ductwork that corrode faster in a chloramine-heavy hall.

Short questions that come up repeatedly — retrofits, testing routines, saltwater pools, what happens during a power cut — are collected in the pool water FAQ.