By Steven Voser

One of the main benefits of hydroponic systems is that they allow us to reuse and recycle water. In turn, hydroponic systems can help drive down our water consumption, which helps both the environment and our back pocket by reducing cost.

Reusing hydroponic water, however, does have its challenges. Old water can carry bacteria, viruses, and diseases that can be passed on from one crop to another. Hence, it’s important to sterilise and clean water before reusing it in order to minimise the risk of infecting and damaging your plants.


Pasteurisation is a process that uses heat to kill bacteria. It’s really common in the dairy industry, where it is used to disinfect milk; but pasteurisation can be used to clean and sterilise a variety of other liquids too, including hydroponic water.

Pasteurisation involves rapidly heating the water. This is done using heat exchangers, which are designed to exchange temperature between two fluids or gases. Without going into too much detail, a heat exchanger uses a fluid or gas (known as the heating/cooling agent) to heat/cool the water in a hydroponic system.

One of the big benefits of pasteurisation is that there’s no need to pre-filter your water. It also helps minimise the buildup of minerals and other biological agents in your water. Unfortunately, these agents can build up in the heat exchangers used to pasteurise the water, meaning they need to be cleaned regularly to keep them working efficiently.

Ozone Generator


Ozonation involves infusing water with ozone (O₃), a natural gas found in high concentrations in the ozone layer, where it is created by ultraviolet radiation from the sun. It can also be created artificially, and used to sterilise and recycle hydroponic water.

Ozonation requires ozone generators to create ozone gas in the grow room. There are two types of ozone generators (corona discharge and ultraviolet), both of which work by splitting O₂ molecules into individual oxygen atoms. These atoms rapidly bind to O₂ molecules to create ozone (O₃), which is then injected into the water to kill any contaminants.

There are many benefits of ozonation. It is by far one of the most effective forms of sterilising water and reacts quickly to any contaminants. It’s also environmentally friendly, and using ozone in your grow room can help prevent disease and pests on your plants (including spiders and mites). However, ozonation is an expensive process. Ozone is also highly corrosive and—when not used properly—can damage equipment in your system.


UV disinfection is another highly effective method for cleaning and recycling hydroponic water. It is completely chemical-free, making it an attractive sterilisation method for growers looking to keep things as natural as possible.

UV water disinfection works by passing water through a radiation chamber holding high-pressure UV lamps. The UV rays from the lamps penetrate molecules in the water (such as bacteria and other harmful pathogens) and destroy their DNA. In higher doses, UV disinfection can also remove chlorine from water (a process known as photolysis). UV radiation is often used to sterilise drinking water, like at the Catskill-Delaware Water Ultraviolet Disinfection Facility in New York, USA, to sterilise drinking water for NYC.

Compared to pasteurisation and ozonation, UV water disinfection is very cost-effective. It is also completely natural and produces no dangerous byproducts. The major downfall to UV sterilisation is that it does not neutralise dissolved organics, chemical contaminants, or inorganic compounds found in water. This means it can’t remove heavy metals, salts, or chlorine at normals doses (high doses of UV are needed for photolysis).

UV Water Purification


All of the water cleansing methods we’ve covered in this article offer different benefits. However, they all come with their limitations too. Choosing one sterilisation method over another will come down to your personal preferences, your budget, as well as the availability of the required equipment in your area and the size of your grow operation.

If you’re trying to minimise cost, UV radiation is likely the best option. Both ozone generators and pasteurisation machines are pricey pieces of equipment. They also come with maintenance costs that will increase the overall cost of your entire operation. UV radiation chambers, on the other hand, are cheaper both to buy outright and run over time, making them ideal for budget-growers.

Both UV and Ozone sterilisation are also better suited for larger operations. Heat pasteurisation is much more expensive and better suited for small growers with large budgets. Ozonation also arguably offers the best results, simply because ozone is such a strong disinfectant. Just remember that it can be highly corrosive and needs to be handled with care.

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