Water Prep For Hydroponic Growing

Water: The Lifeblood of Hydroponics

In hydroponic systems, water does more than just carry nutrients—it is the growing environment. Because plants in hydroponics rely entirely on water for both hydration and nutrition, its quality directly affects their health, growth rate, and resilience. Just like people, plants thrive when they have clean, balanced water. The better the water, the better your results.

How Do You Ensure Clean, Reliable Water in Hydroponics?

If you’ve been researching water treatment for hydroponics, chances are you’ve come across all kinds of advice—some helpful, some... not so much. When it comes to something this important, reliable science should always take precedence over guesswork.

That’s why this guide is built on more than 30 years of hands-on hydroponic farming experience, paired with proven, science-backed methods.

No fluff, no confusing technical terms, and no unnecessary steps—just a straightforward, practical approach to preparing high-quality water that works for any reservoir-based hydroponic system.

Ready to learn how to optimize your water like a pro?

Let’s dive in.

Choosing the Best Water Source for Hydroponics

As a home hydroponic grower, you have several water sources to choose from—each with its own characteristics that can impact plant health and nutrient balance.

City (Tap) Water is the most commonly used source due to its convenience. However, it often contains disinfectants like chlorine or chloramine, which can be harmful to plants if not properly removed. Tap water usually has moderate hardness, meaning it contains a manageable amount of dissolved minerals like calcium and magnesium—minerals that plants need in the right amounts.

Well Water, on the other hand, can vary widely in quality depending on local geology. It often contains higher concentrations of minerals, making it what’s known as “hard water”. While these minerals can be beneficial in small amounts, excess hardness can lead to nutrient imbalances in your system. In many cases, growers use a water softener to reduce mineral buildup.

However, using a water softener introduces its own concerns. Softeners typically replace calcium and magnesium ions with sodium or potassium. While this helps prevent scaling and buildup, excess sodium can be harmful to many plants. If you're using softened water, it’s important to monitor your nutrient solution closely and make necessary adjustments to maintain plant health.

Why Treated City Water Is the Best Choice

With the right treatment, city (tap) water can be an excellent option for hydroponic systems. A high-quality water conditioner—such as PHLO—neutralizes chlorine, chloramine, and even heavy metals, making your water immediately ready to use. There's no need for additional filtration, and you don’t have to let the water sit out to “let the chlorine dissipate.” This makes PHLO-treated tap water a fast, affordable, and reliable solution for most home growers.

Some growers consider spring water as an alternative, but it comes with notable drawbacks. While bottled spring water may contain naturally occurring minerals that support plant health, it's often processed, expensive, and inconsistent. Its mineral content can vary widely between brands and batches, requiring frequent testing and adjustments to maintain proper nutrient balance.

For most home hydroponic setups, the cost, variability, and impracticality of spring water make treated city water a far better long-term solution.

Filtration: A Useful but Not Mandatory Step in Hydroponics

While filtration can improve water quality for hydroponics, it’s not always a necessity beyond basic treatment. The key is balancing cleanliness with the preservation of essential minerals that plants need to thrive. Some filtration methods help remove harmful contaminants without stripping beneficial elements, making them a great option for home growers.

Types of Filtration: Practical Solutions for Home Growers

Two common filtration systems—under-the-sink filters and on-the-faucet filters—provide a simple and effective way to remove impurities while retaining the minerals necessary for healthy plant growth. These options offer cleaner water without requiring nutrient adjustments, making them a straightforward solution for hydroponic systems using city or well water.

Activated Charcoal Filtering: Affordable and Effective

Activated charcoal is a popular filtration choice among hydroponic growers due to its ability to adsorb chemicals, chlorine, and organic compounds. By reducing these impurities, activated charcoal enhances water quality and minimizes substances that could inhibit plant growth or cause damage over time.

This filtration method is cost-effective, easy to maintain, and doesn’t remove dissolved minerals—so it won’t affect water hardness or softness. If you're using city or well water that doesn’t require mineral adjustment, an activated charcoal filter can provide the purification needed without disrupting nutrient balance.

Reverse Osmosis (RO): Maximum Purification with Trade-offs

Reverse Osmosis (RO) offers a high level of purification, removing up to 99% of dissolved salts, minerals, and contaminants through a semi-permeable membrane. RO systems allow growers precise control over nutrient solutions, making them particularly useful for those who require absolute purity in their hydroponic setups.

However, RO filtration comes with trade-offs:

• Higher upfront cost and regular maintenance are required.
• It strips all minerals, making the water soft and completely neutral—which means growers must reintroduce calcium, magnesium, and other essential nutrients to maintain optimal plant health.

For those looking to minimize waste, tankless RO systems provide purification while dramatically reducing wastewater output, making them a more sustainable option.

Final Thoughts: What Works Best?

Filtration can be beneficial, but it’s not always required beyond basic treatment. The best approach depends on your specific water source and system needs. If your tap water is already balanced, a simple activated charcoal filter may be all you need. If you prefer complete control over your water composition, RO filtration can provide a clean slate—with the necessary nutrient adjustments afterward.

With the right filtration strategy, you can create a stable water foundation that supports strong, healthy plants in any hydroponic setup.

Why Distilled Water Is Not Ideal for Hydroponics

Distilled water is a bit of an outlier when it comes to water options for hydroponics—it doesn’t fall neatly into either the “filtered” or “natural source” categories. Unlike filtered tap or well water, which typically retains beneficial minerals, or spring and municipal water, which come with varying mineral compositions, distilled water is completely stripped of all impurities and minerals. It’s not a naturally occurring source, nor is it a filtration method designed to enhance an existing water supply. It’s simply purified water—clean, but empty.

At first glance, this might seem like an ideal blank slate for hydroponics. However, distilled water poses several significant challenges for growers:

• It lacks essential minerals – Key nutrients like calcium and magnesium, which help stabilize pH and support plant development, are completely absent.
• It’s chemically unstable – When exposed to air, distilled water readily absorbs carbon dioxide, forming carbonic acid. This leads to unpredictable and often drastic pH fluctuations.
• Nutrient management becomes more difficult – In hydroponic systems, plants rely entirely on the water for their nutrients. Starting with mineral-free water means growers must artificially and precisely reintroduce every single nutrient, increasing complexity and room for error.

Rather than solving problems, distilled water often introduces new ones—making it more difficult to maintain pH stability and nutrient balance. For most hydroponic setups, it’s not the ideal choice.

Water Maintenance

Regular water changes are essential for maintaining a healthy hydroponic system. Over time, nutrients become imbalanced or depleted, which can lead to deficiencies or toxicities. In addition, stagnant water encourages the growth of pathogens and algae—both harmful to plants.

Generally, it’s recommended to change your water every 2–3 weeks, though the ideal frequency can vary depending on system size, plant types, and growth stage. Monitoring EC (electrical conductivity) and pH can help you determine when a change is needed.

For example, if you notice frequent, hard-to-correct swings in EC or pH, that’s a clear signal it's time to replace the water.

Neglecting water changes can cause:

• Nutrient imbalances that slow growth or cause visible deficiencies.
• The spread of plant diseases due to pathogen buildup.
• Algae overgrowth, which competes for nutrients and can clog your system.

Maintaining a consistent water change routine is critical to a thriving hydroponic garden.

Changing the water in your system doesn’t have to be a chore. There are tools that will make this task fast and efficient. Here is a video showing how fast a water change can be performed in a Gardyn system. However, this method can be utilized in any reservoir system.

Recommended Tools for Water Changes

Conclusion

At UGrowFood, we recommend these proven methods for managing water in a closed recirculating hydroponic system. They are aligned with the natural chemistry of plants and water.

• Avoid adding unnecessary substances to your reservoir.
• Specific enhancers like Shine can be used strategically during flowering.
• Additives such as Cal-Mag are typically not required in Gardyn systems if you’re using proper nutrients and managing your VPD (Vapor Pressure Deficit) correctly.

Maintaining clean water and balanced nutrients is the foundation of successful hydroponic gardening.