How to Clean and Reuse Water From Your Hydroponic Setup

As a grower, you probably chose to grow your cannabis hydroponically for one of three reasons: you want to minimize your water usage, you want to grow better plants with good yields, or you want to grow indoors. And you must’ve already tried everything at your disposal to get the best results.

But did you know that you can clean and reuse your hydroponic water to boost your plant’s growth while minimizing your operation’s carbon footprint further? That’s right — by simply recycling your old hydroponic nutrient solution, you can reap many benefits. 

Depending on how you do it, the process can either be complicated or simple, but there’s more to it than meets the eye. So, let’s dive deeper into cleaning and reusing the nutrient solution of your hydroponic setup in this article. 

Should You Clean and Reuse Water in Your Hydroponic Setup?

If you are growing cannabis hydroponically, you’ll encounter many instances where you have to change or replenish your reservoir water. It could be because of bacteria, mineral imbalance, or algae growth, or it could just be that your water is old. 

Many growers often replenish or change the water when they shift the lighting cycle from the vegetative to the blooming stage, and others change the water between crop cycles (they use the same water for the entire plant’s life stage). Regardless of the situation, you will have to change reservoir water eventually in a hydroponic system. 

The default method here is to toss your old reservoir water down the drain and pour new, clean water into the reservoir. But in some cases, you may want to reuse the same water or simply clean it. In such cases, yes, you can and should clean and reuse your water in your hydroponic setup. 

Here are a few factors you should consider if you want to clean and reuse water:

1. Water Quality

Water quality is crucial in any hydroponic system. If you want to reuse water, you must ensure it’s free from contaminants, including pesticides, heavy metals, and other harmful substances that can affect your cannabis plants. This is why you should frequently check the dissolved oxygen, pH levels, EC, etc., so you can take immediate corrective steps if the quality of the water deteriorates. 

In addition, you can employ water treatment methods to improve water quality and minimize the risk of disease outbreaks. Filtration can remove particulates, while UV sterilization can help kill pathogens and reduce microbial load. Therefore, invest in water treatment equipment and follow maintenance protocols for effective water treatment.

2. Nutrient Balance

In a recirculating hydroponic system, plants take up nutrients. Eventually, these nutrients can become imbalanced. Some nutrients might get depleted faster than others, leading to deficiencies and excessive levels of other nutrients.

To maintain a proper nutrient balance, you'll need to regularly adjust the nutrient solution to ensure that all essential elements are available in appropriate quantities for your plants.

3. Disease and Pest Management

Recirculating water systems can create an environment conducive to the growth of pathogens and pests. One common issue is the development of root rot caused by Pythium and other harmful fungi.

Thus, you have to implement strict sanitation practices, such as sterilizing equipment between plantings and using clean media, which can help reduce the risk of diseases. Also, you can incorporate beneficial microbes or biocontrol agents that can defend against harmful pathogens and pests.

4. pH Regulation

The pH level of the nutrient solution affects nutrient availability to the plants. Reusing water can cause pH fluctuations and the levels gradually shift. So, you have to measure and adjust the pH of the water to maintain it within the optimal range for your specific plant species.

5. System Size and Scale

The size and scale of your hydroponic setup can influence the feasibility of water reuse. You’ll find smaller systems easier to manage, while larger systems require more advanced water treatment and monitoring equipment. If you have large-scale hydroponic systems, it’s best to install automated monitoring and control systems to ensure stable conditions.

Benefits of Cleaning and Reusing Old Water for Hydroponic Cannabis

Cleaning and reusing old water in hydroponic cannabis cultivation can offer various benefits, which are discussed below. 

1. Saves a Lot of Water

Perhaps the biggest benefit of reusing old water in your hydroponic setup is that it can help you save a lot of water. Yes, your hydroponic setup already uses a fraction of the water that you’d otherwise use for a cannabis plant growing in soil, but you can further reduce the water used with this method. This can make your cannabis operation even more eco-friendly. 

If you want to reap this benefit, you must meticulously manage the nutrients and water in your hydroponic system to negate any risk of damage to your cannabis while ensuring the best conditions for it to thrive in. 

2. Minimal Pollution 

Another crucial benefit of reusing your old water is that it will minimize the pollution produced by your cannabis operation. The water you use for hydroponics is concentrated with minerals and nutrients, which is way more than what’s present naturally. 

When you drain this water, there’s a high chance a lot of this may end up in the natural environment and disrupt the ecosystem. Your old yet mineral-rich water can damage your local water pipelines and systems and the natural ecosystem of that area when it ends up in the soil. 

3. Better Plant Growth 

Reusing your old water isn’t just good for the environment, but also for your cannabis plants. Your old water is already rich in nutrients, so for your next cycle, you simply need to clean it and rebalance the nutrients within the solution and it will be fit to be used for your cannabis plants again. This can, over time, boost your plant’s growth while saving you some money in the long run. 

Of course, doing this comes with a risk of contamination, but that won’t be a problem if you follow the right steps. More on this below. 

4. Increased System Automation

Water recycling often goes hand in hand with more sophisticated hydroponic systems. Automated systems can monitor and adjust key parameters such as nutrient levels, pH, water temperature, and lighting schedules. This level of automation can help optimize plant growth, save time, and reduce the need for constant manual intervention.

Through the use of sensors, controllers, and specialized software, you can create highly efficient, precise, and stable growing environments, maximizing the potential of cannabis plants.

Disadvantages of Reusing Water for Hydroponics

Hydroponic setup is revolutionary and it can help you grow cannabis plants in an efficient and sustainable manner, and one of its biggest advantages is that you can always recycle your water to minimize the environmental damage and nutrient and water conservation. However, recycling may not always be the best option as it comes with some downsides, which are as follows. 

1. Risk of Toxicity from Nutrients and Minerals 

Hydroponics, by nature, is a very precise way to grow plants. This precision comes at a cost — if anything is out of whack even by a small margin, it can lead to significant problems for your cannabis plant, and the nutrient balance in the water is no exception. 

Your water is already loaded with various nutrients and heavy metals like copper, zinc, and lead. These minerals can pose a serious risk to your plant if they are given in a dose higher than required. So, when you reuse water, you must ensure that the nutrients are balanced properly and are not present in higher quantities than required. 

2. Controlling the Nutrient Balance can be Tricky

Let’s be honest, controlling the nutrient levels in water for hydroponics is already tricky, and it gets trickier if you have to reuse your water. Even if you add more water, it may also contain several minerals naturally, especially if you use tap water. So, if you recycle old water for hydroponics, you need to keep a close eye on the nutrient levels in your hydroponic system. This is a tedious process. 

How to Clean and Reuse Your Old Water in Hydroponics?

Weighing the pros and cons of recycling your old hydroponic water, you have finally decided to go down this route for your plant and the environment (and your wallet). So, let’s start with cleaning your old water. Do note that this method demands some equipment, which may not be practical for a hobby grower, except for one. Here is how you can clean your hydroponic water for cannabis. 

1. Pasteurization 

If you don’t reuse your water properly, you can give your plant water that does not contain enough nutrients or bacteria or algae that can infect your plant. So, treating your old water is crucial before you give it back to your plants, and one of the most popular methods of doing so is the pasteurization process.

In this process, the water is heated to a high temperature for half a minute, which sterilizes the water by eliminating all the harmful bacteria and microorganisms in the water. And to conduct this process on your setup’s old water, you’ll need a heat exchanger. This device transfers heat to the water. 

Here, you first need to preheat the heat exchanger, which reduces the risk of thermal shock. Once the device is preheated, you have to slowly heat the water until it reaches the pasteurization mark. At this temperature, the water must be exposed to the heat for at least half a minute before letting it cool down. 

One major downside of the pasteurization process, despite it being an efficient way to clean the water, is that the nutrients can get clogged in the heat exchanger over time, which can be damaging to the device. To prevent this, you need to clean and service your heat exchanger regularly. 

Plus, the pasteurization process is expensive and best suited for commercial cannabis growers.

In summary, here are the pros of the pasteurization process:

• It sterilizes and cleans the water properly
• The heat exchanger can be found fairly easy 
• And the machine is quite straightforward to use 
• The process also removes all the minerals and nutrients from the water 
• It is also not toxic for the environment, you, or your plant 

2. Ozonation 

The second common process of cleaning and reusing old hydroponic water is ozonation, which is also known as ozone sterilization. This process eliminates contaminants and microorganisms from water, which can otherwise damage your cannabis plant. 

Ozone is a type of gas made up of three oxygen molecules. This gas occurs naturally in the environment at the ozone layer, which protects our planet from harmful UV radiation from the sun. But when this gas is present in higher concentrations, it can also create UV radiation that can be used to recycle water for your hydroponic setup. 

For the ozonation process, you need an ozone generator, which comes in two types. The first is a corona discharge (CD) generator or UV generator. Both these generators produce the same result but in a different manner. 

For example, a corona discharge generator uses a high voltage of electricity to generate ozone and is also hard to operate since it requires some technical knowledge of the machine. On the other hand, a UV generator or a UV lamp uses ultraviolet light to generate ozone, and thereby, it is easier to operate and much more energy-efficient than the other one. 

To summarize, here are some pros of ozonation:

• It is a reliable method to clean hydroponic water
• The process does not create any toxic byproducts 
• The process also breaks down the minerals in the water

However, there are some cons of ozonation, too, like:

• Specialized ozone generators can be expensive 
• It is only suitable for a large commercial operation 
• Requires technical expertise of the machine and its workings 

3. UV Disinfection

If you are a home grower, the methods mentioned above are overkill, but that doesn’t mean you are out of options. The best way to recycle old hydroponic water for home growers is to use UV disinfection. 

This process uses UV-C radiation to kill any bacteria or pathogens that may be present in your hydroponic water. The basic principle of this is: UV-C radiation disrupts the genetic material of bacteria and viruses by penetrating their cell walls, thereby preventing them from reproducing. 

For this method to work efficiently, you need to give your water a total UV dose, and you also require a radiation chamber and disinfection unit depending on how much water you want to clean at a time. 

The UV disinfection method has various benefits for home growers, even a few that the methods mentioned above lack. Here are some of the benefits:

• The entire process is chemical-free 
• It does not produce any by-products 
• It does not affect the nutrient balance in the water
• It is cheap and easy to carry out even for a beginner 

Other Less Common Methods of Cleaning Hydroponic Water

For many growers, the above-mentioned methods may not work due to financial constraints or the effort and skills required to perform them. In such cases, you can consider using some other methods to recycle your hydroponic water, which is mentioned below. 

Remember, these methods are not recommended unless you have run out of options since they never disinfect the water completely. 

1. Ultrafiltration

This method is also referred to as membrane filtration and it works on reverse osmosis. Essentially, this process involves the use of various porous membranes that filter out bacteria and other solids from the water. 

The downside of this method is that it is not 100% effective and, over time, the filters can clog up, making it even less effective at cleaning the water. Plus, this process also removes fertilizer salts, which could otherwise be beneficial for your cannabis. 

2. Hydrogen Peroxide

Hydrogen peroxide is also a good option to choose as it works on the same principles as ozone, but it is much less effective than the latter. So, hydrogen peroxide does clean the water of viruses and fungi but it is relatively useless against bacteria. So, if you use this method, your water won’t be completely disinfected. 

Also, if you accidentally use too much hydrogen peroxide, you can do more harm than good. High levels of hydrogen peroxide can be toxic for cannabis plants, so it’s crucial that you neutralize them before using them. 

Choosing the Right Method for You

Choosing between these methods need not be confusing at all. If you are a commercial grower, you can choose either pasteurization or ozonation, but you may have to determine the resources at hand. Ozonation is complicated and requires specialist knowledge and skills to operate the machine, so it is only suitable for growers with a skilled team and an elaborate commercial setup.

On the other hand, home growers should always go for UV disinfection as it is the easiest and most effective for smaller setups. But as a last-ditch effort, hydrogen peroxide and ultrafiltration can also work. In any case, avoid the iodine method — just because it kills human viruses does not mean it will kill plant viruses. 

How to Maintain Your Hydroponic Water?

If you are recycling your hydroponic water, it is recommended that you maintain the same properly so you can use it for longer. Ideally, this step should always follow recycling, and here are some steps to help you do the same. 

1. Keep the Nutrient Solution at the Right Temperature 

Temperature is crucial not just for your cannabis plants but also for the nutrient solution. If the temperatures are too high or low, the nutrient solution can start running into problems. So, maintain an ideal temperature of 65°F to 75°F ( 18°C to 24°C). 

Some of the problems that may occur in the water due to improper temperatures include:

• If the temperature is too hot, the water can lose oxygen faster
• Low temperatures can slow down the growth of your plant
• Higher temperatures can lead to algae or fungal problems within the reservoir 

Some of the best ways of maintaining the right temperature of the reservoir water are to use a chiller, place the reservoir in a shade, or paint it white or black, depending on the ambient temperature. Also, it is recommended that you use a large reservoir since a large one suffers from fewer temperature fluctuations. 

2. Recycle the Hydroponic Water Regularly 

Once you recycle your hydroponic water, no matter the method you used, it is still technically old water. So, it is always a good idea to recycle it regularly. Depending on your preference, you can either recycle the hydroponic water weekly or monthly. 

Additionally, invest in a good EC meter as it is a reliable way to determine the concentration of nutrients in the water. It won’t tell you the exact ratios of the nutrients, but it will at least tell you if there is any nutrient buildup in the water. 

3. Regulate the EC and pH 

Speaking of EC, you should always check the pH and EC of your nutrient solution. This can be done with the help of a pH meter and an EC meter. We mentioned why EC is crucial, but pH is just as crucial. If the pH is not ideal, your cannabis plant’s roots may fail to absorb some nutrients, which can lead to nutrient deficiencies or toxicity. 

The best pH for a hydroponic cannabis plant is between 5.5 to 6.5, and the best EC for the same is between 1.2 to 2.0.

If the pH is off, you can use a pH up/down solution to manipulate the pH of the solution. These solutions are easy to use, but if the pH keeps fluctuating all the time, it may be a sign that something is wrong with your hydroponic setup. In most cases, there is a mineral buildup somewhere in the chamber or the plumbing, which is influencing the pH levels. 

4. Aerate the Hydroponic Water

Oxygen is crucial for your cannabis plant’s roots, and if you are using a hydroponic setup where the roots are submerged in water, you must aerate the water to ensure the roots get enough oxygen at all times. 

Ideally, for a gallon of hydroponic water, you should add a liter of air per minute. This can be done using an aquarium airstone. 

5. Clean the Hydroponic Setup

When recycling your hydroponic water, it is also a great time to clean your hydroponic system, including the reservoir. This is a sanitization process, nothing less, so aim to clear out any dead plant matter, clean up the air filters, wash the reservoir, and make sure everything is clean in the setup. Here’s how you can do that. 

For the best results, you can use a hydrogen peroxide plus water solution, and as a safety precaution, always wear gloves. Hydrogen peroxide can cause skin burns. An ideal ratio of hydrogen peroxide to water should be 125ml of hydrogen peroxide to five liters of water. Fill your reservoir with this mixture. 

Start by disassembling your hydroponic setup, including the pumps, plumbing, and any other part that is related to water or irrigation. Then, use the mixture-filled reservoir to clean all the smaller parts; use a brush to scrub everything down. 

Next, clean the substrate by following the manufacturer’s recommendations. Since all substrates are different, they require different cleaning methods. 

Finally, use a fresh hydrogen peroxide solution to scrub down the major components of your hydroponic system, like the chambers and the reservoir. That’s all you need to do to clean your hydroponic setup. 

Summary: How to Clean and Reuse Water From Your Hydroponic Setup?

As you can see, cleaning and reusing water from your hydroponic setup can be a terrific choice. It helps you save a lot of water and money, minimizes your cannabis operation’s pollution, and, in some cases, it can even help you grow better, healthier cannabis plants.

Choose pasteurization if you have a moderate commercial setup and ozonation if you have a massive commercial setup, and if you are a home grower, use UV disinfection as it works just fine for smaller operations. 

Lastly, remember to maintain your recycled hydroponic water by keeping the hydroponic setup clean, maintaining the nutrient levels along with pH, and aerating the water. Do these and you can reuse and recycle the nutrient water of your cannabis plant almost perpetually. 

However, clean and recycled water isn’t everything. Hydroponic cultivation of cannabis is a seemingly endless subject and there are always newer possibilities to improve your cannabis yields. If you want to become a better hydroponic grower, stay tuned to our blog. We regularly post growing guides that can help you take your cannabis cultivation to the next level.