If you are weighing up low-pressure vs medium-pressure UV systems for treating pool or drinking water, the decision is more consequential than the price tag suggests. Both technologies use ultraviolet light rather than pumping more chemicals into the water, and both promise cleaner water without the harsh by-products of chlorination. Yet under the surface, low-pressure and medium-pressure UV systems work in fundamentally different ways — and that difference determines whether your disinfection is reliable, permanent, and able to tackle the toxic compounds that build up in a busy pool.
This guide explains how UV disinfection works, where the two technologies diverge, and why a broad-spectrum medium-pressure system is the only one recognised by the relevant German pool standard for tackling bound chlorine. By the end, you will know exactly which approach suits your water — and why “it kills germs” is not the full story.
Essential takeaways if you're short on time
- Both use UV-C light, but the spectrum differs. Low-pressure lamps emit a single wavelength (253.7 nm); medium-pressure lamps emit a broad spectrum across the entire germicidal range (roughly 200–600 nm).
- A wider spectrum means more thorough disinfection. Because different microbes and compounds are destroyed by different wavelengths, broad-spectrum UV removes a far wider range of contaminants.
- Photoreactivation is the weak point of low-pressure UV. Some microbes can repair single-wavelength UV damage with the help of light and enzymes — then carry on multiplying.
- Medium-pressure UV makes inactivation permanent. It damages not only DNA and RNA but also enzymes and proteins, so reactivation is no longer possible.
- Only medium-pressure UV (UV-M) is recognised by DIN 19643 for reducing bound chlorine, including toxic trichloramine, in pool water.
Why UV light is used to disinfect water
Ultraviolet light is invisible to the human eye, yet it has become one of the most elegant tools we have for cleaning water. The story goes back further than most people expect: the first successful use of UV light for water treatment took place in the United States as early as 1916, once scientists realised that short-wavelength radiation could break microbes down. More than a century later, the principle is the same — only the engineering has caught up.
There are three bands of ultraviolet light: UV-A, UV-B and UV-C. Only UV-C, the shortest and most energetic, is suitable for effective disinfection. When a microorganism passes by a germicidal lamp, UV-C radiation scrambles the information stored in its DNA. The cell survives the encounter but can no longer replicate, so the population collapses. The water that flows out the other side stays transparently clean — without a single extra gram of chemicals.
The main advantages of disinfecting water with UV radiation:
- reaction time measured in seconds
- no reaction vessel or holding tank required
- low operating costs
- no change to the original composition of the water
- no effect on the taste or odour of the water
- no harmful disinfection by-products created in the process
The heart of any UV system is a specialised germicidal lamp that converts electricity into ultraviolet radiation. Water flows continuously through the lamp chamber, where it is bathed in UV light. In short, modern UV treatment is simply a cleaner, greener alternative to traditional disinfectant chemicals — which is exactly why it has become so sought after for both pool and drinking water. If you have ever wondered what really lurks in pool water, our overview of unknown health risks in swimming pools puts the problem in context.
The difference between low-pressure and medium-pressure UV systems
When you disinfect with ultraviolet light, one rule does most of the heavy lifting: the wider the spectrum of wavelengths a UV system can emit, the more effectively it eliminates pathogens. The logic is straightforward. Each substance and each microorganism is broken down by a different wavelength, so treating water with broad-spectrum UV-C inevitably removes a wider range of harmful substances than a single, fixed wavelength ever could.
This is where the biggest difference between low-pressure and medium-pressure UV systems lies. Low-pressure lamps emit UV radiation at only one wavelength: 253.7 nm. It is a useful, well-targeted wavelength — but it is just one note in a much larger chord. Medium-pressure lamps, by contrast, emit a continuous spectrum across the entire germicidal range, roughly 200 to 600 nm. Instead of a single tool, a medium-pressure system effectively carries a whole toolkit.
The two technologies also differ in how the lamps themselves are built. Inside a low-pressure lamp, a vacuum is created and the tube is then filled with a low-pressure gas, resulting in an internal pressure of around 1 to 10 mbar. The manufacturing process for a medium-pressure lamp is different: the tube is filled with gas to create a much higher internal pressure of 1 to 5 bar, which is precisely what allows it to emit that broad, high-intensity spectrum.
For home pools and hot tubs, the medium-pressure approach is delivered by the ProfiPure UVM lamp, which uses UVM technology to disinfect water in pools up to 200 m³. Put simply, a medium-pressure UV system removes the same contaminants a low-pressure system does — and then keeps going, eliminating a wide range of additional substances a single wavelength leaves behind.
Medium-pressure UV for healthy pool water
ProfiPure UVM
New-generation medium-pressure UV lamp for healthy water in home pools and hot tubs up to 200 m³.
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Medium Pressure UV lamp LifeUVM03
250 W replacement medium-pressure lamp for the ProfiPure 100 and 200 models.
View price →Medium-pressure UV systems destroy bacteria and toxic trichloramine
If you have any experience with low-pressure UV systems, you have probably noticed that their effectiveness is not quite as absolute as the brochures suggest. The reason is evolutionary. Over millions of years, microbes have developed an efficient natural defence against ultraviolet light, and some are remarkably resilient. With the help of light and a set of specialised enzymes, they undergo a process called photoreactivation: they repair the very DNA the UV lamp damaged, recover, and carry on multiplying in the water.
This possibility of microbial reactivation after low-pressure UV treatment is one of the most frequently raised concerns about the technology. Anyone using UV to disinfect water wants to be absolutely certain that treatment is reliable and, above all, permanent. A single-wavelength low-pressure system simply cannot guarantee that.
That is exactly why the current version of the German standard DIN 19643 for swimming pool water treatment states clearly that only UV-M — in other words, medium-pressure UV systems — can reliably disinfect pool water while also reducing the concentration of bound chlorine, including dangerous trichloramine. That trichloramine is no minor nuisance: it is the compound behind the sharp “swimming pool smell” and a recognised respiratory irritant. We explain it in detail in our article on trichloramine, the hidden danger in your pool.
This recommendation is not arbitrary. The research shows that broad-spectrum medium-pressure UV light, made up of many wavelengths at once, causes irreparable damage to microorganisms. Beyond DNA and RNA, it reliably destroys the enzymes and cellular proteins a microbe would otherwise need to repair itself. With the repair machinery gone, reactivation becomes impossible — and microbial elimination becomes permanent. That same broad spectrum is also what allows the system to break down bound chlorine, which a low-pressure lamp leaves untouched.
The main advantages of medium-pressure UV systems:
- water disinfection is permanent, with no microbial reactivation
- removes chlorine-resistant pathogens such as Cryptosporidium parvum and Giardia lamblia
- destroys toxic trichloramine and the unpleasant “pool” odour that comes with it
- reduces the overall use of pool chemicals
- does not irritate the eyes, skin or mucous membranes
- lowers the risk of asthma developing in children
- an ideal water-treatment solution for allergy sufferers, asthmatics, atopic individuals and young children
- low operating costs — even lower than conventional UV systems
- an environmentally friendly, “green” approach to disinfection
- easy to install and maintain
For pool owners who want to step away from aggressive chemistry altogether, medium-pressure UV pairs naturally with gentler maintenance routines — the same philosophy behind our guide to cleaning a pool without chemicals.
A (r)evolution in the lifespan of medium-pressure UV systems
For a long time, the one genuine weakness of medium-pressure UV systems was their lifespan. Even today, ordinary broad-spectrum (UVM) lamps running on standard magnetic ballasts typically last only around 4,000 to 8,000 operating hours. The number of starts matters too: frequent on-off cycling shortens lamp life, which is why many manufacturers factor the number of cycles into their warranty conditions.
Installation requires a little engineering care as well. With medium-pressure UV systems, you must maintain a minimum flow rate around the lamps to keep them continuously cooled, and a safeguard that automatically switches the lamp off if flow stops is essential — otherwise the reactor can overheat. None of this is difficult, but it is the kind of detail that separates a reliable installation from a troublesome one.
The good news is that the headline weakness has now been addressed. Modern medium-pressure UV systems on the market last dramatically longer than they used to, and the credit goes to the Czech company Lifetech, recognised worldwide as a specialist in ozone, UV and AOP technologies (AOP = advanced oxidation processes). Lifetech developed advanced electronic power supplies built around its own LifeAGE® technology, which has significantly extended the life of medium-pressure LifeUVM® lamps.
What does that mean in numbers? Medium-pressure UVM systems from Lifetech will reliably run, on average, for around 18,000 hours — and users proudly report installations where the lamps have run for up to 30,000 hours, setting new records. The single biggest objection to medium-pressure UV, in other words, has largely been engineered away. When the time does come to replace the lamp, the LifeUVM03 medium-pressure lamp is the direct, manufacturer-supplied replacement for the ProfiPure 100 and 200 models.
So which UV system should you choose?
If you only need to reduce the general microbial load in relatively clean water, a low-pressure UV system will do a competent job at a lower upfront cost. But for pool water — where bathers continuously add organic matter, where bound chlorine and trichloramine accumulate, and where reliability is not negotiable — the broad spectrum of a medium-pressure system is the superior choice. It disinfects permanently, tackles compounds a single wavelength cannot touch, and is the only technology DIN 19643 recognises for reducing bound chlorine.
The choice between low-pressure and medium-pressure UV systems, then, is really a choice between “good enough for clean water” and “built for real-world pool conditions”. For families with allergy sufferers, asthmatics or small children in the household, that distinction is worth taking seriously. At nanoSPACE, we recommend medium-pressure UV not because it is the more expensive option, but because it is the one that keeps water genuinely — and permanently — safe.
Frequently asked questions
What is the main difference between low-pressure and medium-pressure UV systems?
Low-pressure UV lamps emit radiation at a single wavelength (253.7 nm), while medium-pressure lamps emit a broad spectrum across the entire germicidal range (roughly 200–600 nm). Because different contaminants are destroyed by different wavelengths, the broad-spectrum medium-pressure system removes a wider range of substances and inactivates microbes more thoroughly.
What is photoreactivation, and why does it matter?
Photoreactivation is a natural repair process in which some microbes use light and specialised enzymes to mend UV-damaged DNA and resume multiplying. It is the main weakness of single-wavelength low-pressure UV. Medium-pressure UV prevents it by also destroying the enzymes and proteins needed for repair, making disinfection permanent.
Can a UV system remove trichloramine from pool water?
Yes — but only medium-pressure (UV-M) systems. The German pool-water standard DIN 19643 recognises only UV-M for reducing bound chlorine, including toxic trichloramine, the compound responsible for the harsh “pool smell” and for eye and respiratory irritation.
How long does a medium-pressure UV lamp last?
Standard UVM lamps on magnetic ballasts typically last around 4,000–8,000 hours. Modern systems using Lifetech's LifeAGE® electronic power supplies last far longer — on average around 18,000 hours, with some installations reportedly reaching up to 30,000 hours. Frequent on-off cycling shortens lamp life.
Is UV-treated pool water safe for children and allergy sufferers?
Yes. Because medium-pressure UV reduces the use of pool chemicals and removes irritants such as trichloramine, the treated water does not sting the eyes, skin or mucous membranes. It is considered an ideal solution for allergy sufferers, asthmatics, atopic individuals and young children, and is associated with a lower risk of childhood asthma.
