Impact of Tap Water in Hydroponics and How to Reduce its negative effects

Can I use tap water for hydroponics?

Water is the basis for growing plants with any method, but with hydroponics it plays an even more significant role. The contents of your water before you add nutrients has a huge impact on how nutrients interact, and how your solution ultimately affects your plants.

Understanding the impact of tap water and how to reduce its negative effects will result in vigorous growth and larger yields in your hydroponic garden.

The Role of Water in Hydroponics

In a hydroponic system plants grow only in water. There is no soil or other organic surrounding that acts as a barrier for plant roots.

This means that there is a direct interaction between plants and the water they uptake, which also contains all required nutrients for growth.

Without a protective barrier to soak up excess nutrients or chemicals, if it’s in the water, it will get into your plants.

So if you’re using tap water in your hydroponics system, whatever is in your tap water will get into your plants.

Using Tap Water – What’s the Big Deal?

If you're using tap water for hydroponics, it’s likely due to necessity, where else would you get your water from?

So you must use it, but if you understand what’s in your water, you can do a lot to control and reduce its negative impact. 

What's wrong with using tap water in hydroponic cultivation?

Chlorine and Chloramines

Chlorine and chloramines are both added by water treatment plants to kill bacteria and pathogens harmful to humans. While this is a good thing, it can be very harmful to plants.

These chemicals will kill any beneficial bacteria or fungi in your system. These microbes help to increase the amount of nutrients that plants can uptake.

Without these beneficial organisms, plants get less nutrients, therefore grow smaller and yield less

Although plants need chlorine in small amounts, tap water contains much more than plants regularly need. To add to this, many hydroponic nutrients contain chelates, which help keep nutrients suspended in water.

When chelates come into contact with chlorine, they bond and further increase the amount of chlorine taken up by plants.

Too much chlorine causes a nutrient toxicity (too much of a nutrient), which stunts plant growth.

Chelates in Hydroponic Nutrients

Chelates are used in hydroponics to help plants uptake more nutrients. Certain nutrients will not remain suspended in water, and will combine with one another to form compounds that plants can’t uptake.

Chelates remedy this issue by forming bonds with these nutrients that keep them suspended in the water, and make uptake by plants easier.

For nutrients you want getting into your plant, this is great! But certain undesirable elements in tap water are more easily absorbed by plant roots because of chelates.

When chelates come into contact with chlorine, they bond and allow more chlorine to enter your plants. This causes toxicity as it gives the plants much more chlorine than they need.

Hard Water

Tap water may be considered ‘hard’, which means it has a high ppm. This means that there are extra dissolved elements in the water, which can end up in your plants.

Water with a ppm (parts per million) of 150 or greater has a lot of Calcium and Magnesium in it. Although plants need both nutrients, the molecules of these elements in tap water are too large to be absorbed by roots. This means they will collect in your system and stain and clog every part of your system.

By starting with a high ppm, you have less room to add nutrients to your system. If you want to feed your plants an 800PPM solution, but have 250PPM out of the tap, you have little room left. This can make it easy to burn your plants (toxicity) or unintentionally not provide them enough nutrients.

PH Problems

It is relatively unlikely that your tap water will come out at the perfect pH to water your plants with. This means that you need to adjust the pH in order to properly feed your plants.

Adjusting pH usually involves adding an acid or a base to lower or raise your pH. The chemicals in most pH adjusters also kill any microbes in your system, resulting in the same problem caused by chlorine.

Some pH adjusters contain salts of Phosphorous or Potassium. Plants also need these, but by adding excessive amounts you can cause a toxicity or lockout of another nutrient.

Solutions for Using Tap Water

So as we have discussed, there are problems with using tap water in hydroponics. But thankfully, there are many solutions to using it.

How to Remove Chlorine from Tap Water?

Chlorine can easily be removed from your tap water by allowing it to sit outside in direct sunlight for 24 hours. The UV rays will break down the chlorine, thus removing it from your water.

This can be problematic if your system is large, so using a carbon filter or Reverse Osmosis (RO) filter would be more appropriate.

Other options include additives like campden tablets and sodium thiosulfate (commonly used in aquariums).

What is the Best Way to Remove Chloramines from Your Water?

Chloramine is more difficult to remove than chlorine. It will not evaporate for a long time, and so must be filtered out. Carbon filters or an RO system are the best options to remove chloramine.

Not all tap water contains chloramine, to find out, just call your municipal water supply and ask if chloramine is added to the water.

How to Soften Hard Water

Excess salts in tap water must be mechanically removed using a carbon filter, or a reverse osmosis system.

You can also dilute your tap water with distilled or RO water to lower your PPM.

Solving pH Problems

Filtering is the best solution for this issue. Filtering will remove excess salts and usually produces water with a pH around 6.0.

This is ideal for hydroponics, and at the very least will reduce the chance of adding too much salt-laden pH adjuster.

Recommendations for Tap Water

The following are a few recommendations that will help in diagnosing and treating your tap water.

Reverse Osmosis SystemHydroLogic 150 GPD Stealth Ro150 RO Filter

RO systems come in many shapes, sizes, and prices; this unit is reasonable priced around $150. I have used this unit myself for both hydroponics and aquaponics, and it has served me well. These systems will filter out all unwanted contaminants from your tap water and leave you with nearly pure water, perfect for hydroponics.

The downside to an RO system is the upfront cost and it wastes 2-3 times the amount of water than it filters. There is also upkeep which requires that you replace the carbon, sediment, and membrane filters eventually.

Faucet Filter: Brita Tap Water Filter System

A filter attached directly to your tap is a great way for smaller growers to efficiently remove chlorine and excess salts. For $20 to 30, this filter will easily make your tap water safe to use with your plants.

PPM Meter: HM Digital TDS-4 Pocket Size TDS Tester Meter with 0-9990 ppm Measurement Range

A PPM meter is already essential in hydroponics, so if you don’t have one, get one! This is just an example of a good quality meter for a good price. With a ppm meter, you can easily check the ppm of your tap water to check if the ppm is too high. You can also (and should) use a ppm meter to regularly check the ppm of your hydroponic solution. 

pH Meter: Bluelab PENPH pH Pen

As the name suggests, you can use these to monitor your pH. Use this to determine if your tap water pH needs to be adjusted. As with the ppm meter, this is just a great tool to have in hydroponics. This meter is pricier, but cheaper pH meters are prone to inaccuracy and can stop functioning quickly.

you use tap water for hydroponics? The Verdict

After looking at what’s in tap water and how it can affect your plants, it’s clear that tap water and hydroponics don’t mix. But that doesn’t mean you can’t grow hydroponically with it.

If you follow the recommendations outlined here, you can make any water safe for your plants. Ultimately, how you remove the contaminants in tap water will depend on how big your operation is.

If you’re a hobbyist, using sunlight to remove chlorine and a drinking filter to lower ppm should work fine. If you’re a bit larger, you’ll want to stick with a filtration system.

Impact of Tap Water in Hydroponics and How to Reduce its negative effects using Ro water

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Lindsey Hyland grew up in Arizona where she attended University of Arizona’s Controlled Environment Agriculture. She has supplemented her formal education by working on various organic farms, including spending a semester abroad in India.

Growing and/or raising just about anything gets her excited. She is especially passionate about environmental justice and low-tech, sustainable ways to better run small-scale farms and homesteads. Lindsey started Urban Organic Yield to discuss gardening tips and tactics.

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