Aquadome in City of Playford, South Australia

Gastro Is On The Rise

Almost 5 times the number of Gastroenteritis (or Gastro, the infectious condition that affects the stomach and intestines) cases have been recorded in South Australia in the first 3 months of 2024 compared to the same period in 2023. The total number of nationwide cases is up 1333% on a 14-day period in February, when compared to the same time last year. The extended warm weather we experienced from January through March resulted in more people frequenting their local pools. Other than normal summertime temperatures, we can thank the current El Niño season Australia is experiencing. El Niño events are associated with warm, dry conditions (think El Ni-ÑO rain).


Consequently, a higher bather load (more people in the pool) invites more opportunity for contaminants to enter the water. Chlorine is very efficient at disinfecting water, and at the correct levels, along with pH, maintains a safe environment for all to enjoy. However, there are microorganisms that Chlorine can’t work its magic against – and that includes microscopic parasites like Cryptosporidium.

Crypto, as it is more commonly referred, is the leading cause of diarrheal disease in bathers of infected swimming pools and natural bodies of water. It is caused by the ingestion of water from the introduction of faecal matter, most predominantly in accidental faecal release (AFR)  but also when bathers either don’t shower before entering the pool or return to swimming too soon after being unwell (the recommended exclusion period is a minimum of 2 weeks as directed by SA Health). It impacts the elderly and infants the more seriously due to weakened immunity.

Treatment of Cryptosporidium in pools is complex as the parasite is resistant to the safe levels of chlorine in water typical of public pools. This means that pools need to close and increase the concentration of free chlorine for a specified duration to neutralise the parasite. This costs time and money in the pool being unavailable and the increased need of chemicals. Please refer to SA Health’s factsheet outlining the requirements for the specified chlorine concentrations and time to adequately disinfect.


Naturally, the best option is prevention via better education of patrons around showering before entering the pool and not swimming within 14 days of being unwell. But better still is the introduction of sophisticated plantroom equipment to mitigate unfortunate incidents in the first place.

The use of a UV system, which can be retrofitted to an existing filtration system and is very cost effective, doesn’t reduce the need for chlorine but works alongside it to eliminate harmful parasites that aren’t neutralised by standard chlorine concentrations. Another option is the installation of an Ultra Fine Filter (UFF), which can remove particles from water down to 1 micron in size – particles smaller in size than many viruses (Cryptosporidium Spp. Oocysts measure 4.2 to 5.4 microns).

So which option is best? The education of patrons will never stop being necessary to portray the consequences of swimming when unwell.

Hydrilla are installing more and more UFF in both new and existing plantrooms as the benefits to both the operators and patrons are understood. These filters incur a high capital investment but come with several benefits including energy reduction, chemical use reduction, water use reduction, and greater ease of use for pool operators. The installation of an UFF is not a quick, nor simple job, however. Changes to plumbing and plantroom layout are among some of the complexities of changing filtration type. UFF work by using an inert media with a very high surface area to capture particles from within water, down to microscopic sizes, including Cryptosporidium. The capacity of sand and cartridge filters to remove microscopic particles is limited to particles down to 8 microns in size.

Conversely, the installation of a UV system can occur in less than a few days, meaning pool closures are at a minimum, and the capital investment is a fraction of the cost of installing UFF. A UV system can be retrofitted in place (in an existing plantroom) and works to destroy both chloramines and inactivates parasites through a process called photodegradation or photolysis. The wavelength of UV light scrambles parasitic DNA, interrupting the reproduction cycle, subsequently causing microbe death.

Hydrilla have become the South Australian commercial UV system specialists, having retrospectively installed UV systems in many facilities (outside of new build installation as well). Other than excellent water quality, the main purpose of installation is reduction in chloramines. Chloramines are responsible for the ‘Chlorine’ smell evident at some pools and can bring on allergic reactions and asthma in some people, so reducing their concentration in pools is important.

UV system in place at Uni Sa's Pridham Hall

UV system installed at Uni SA’s Pridham Hall, South Australia

UV system installed at Aquadome in City of Playford

One of the three UV systems installed at Aquadome in City of Playford, South Australia






















Below is a comparison chart of a few key factors when thinking about UV and UFF, where a score of 1 = least favourable, 5 = most favourable.

Capital Cost52
Installation Time52
Ease of Use44
Annual Operation Cost44
Local Support54

It is worth noting that a UV system and UFF can operate together, further reducing the risk of Cryptosporidium outbreak, while simultaneously reducing chloramines.

True for all equipment, a correctly sized UV system is probably the most important consideration. Many of Hydrilla’s UV installations have been replacing poorly sized and scaled equipment, leaving the client initially wondering what they have invested in since they aren’t achieving the results they were anticipating. After installing or replacing a UV system, the results are almost immediate – with chloramine levels reaching break point.


Gastro and Cryptosporidium are generally avoidable with ongoing patron education. However, to supplement this education, the use of some clever technology is the next best option. A modest capital outlay, minimal user disruption, and often instant results make a UV system an excellent investment to ensure your facility is both operating to the highest level and a safe and welcoming space for patrons.

For more information, including cost of UV installation at your facility, we welcome you to get in touch today.

Disclaimer: The information in this article is based upon the experience and knowledge of public swimming pool water treatment systems unique to Hydrilla Pty Ltd. This information should not be misinterpreted as advice, and the reader is encouraged to do their own research and form their own opinions with respect to Ultra Fine Filtration and UV systems which will be suit their individual situation. Seeking the services of an accredited aquatic consultant is essential. Hydrilla Pty Ltd has no specific affiliations with any brands, and images listed here are for visual representation only. Additionally, should a gastro outbreak be linked to a public swimming facility, it is important to note that SA Health may still require a pool closure and additional chemical dosing in line with Contact Time, irrespective of a UV system. 

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