Aug 14, 2020

Should I Filter My Grow Room Water?

Your water source is going to be the predicting factor dictating how you will need to filter. Water, in its purest form, is composed of two hydrogen atoms and one oxygen atom (H20). However, water from a tap, well, or spring is rarely this pure.

There are often minerals, and other substances, dissolved in water that can be both good and bad for plants. Just because water is safe to drink, does not mean it is completely safe for your plants. Don’t fret, these “grow contaminants” are easy to take care of yourself.

Chlorine and Chloramine

The largest obstacle when it comes to treated water is chlorine. Water treatment facilities have always added a little chlorine to the water supply to ensure that humans are not ingesting dangerous microbes. In the last few decades, this process has changed a bit.

Now, it is common practice to treat our drinking water with chloramine, a combination of chlorine and ammonia. Unlike chlorine, chloramine will not dissipate into the air if left to sit out for a while. Chloramine must be physically filtered out of the water.

What’s the Problem?

Chlorine kills microbes and can't differentiate between good and bad microbes. This presents a serious issue for growers that take advantage of beneficial fungi and bacteria. Be aware that some additives or biological pesticides can be living microorganisms that won’t take well to chlorine in tap water. Another issue associated with chloramine, it may make the water more acidic. Over time this can change the pH of your soil. Some evidence also indicates that chlorine, in any form, may stunt root growth in plants.

Types of Filters

The filtration method that’s best for you will depend on a couple of things—how much water you need to purify, time consumption, cost, and labor.

Reverse Osmosis or RO filters

This type of filter removes pretty much everything. It is an excellent choice for hydroponic growers. If large amounts of water are required for your operation an RO filter can be installed at the source. The HydroLogic Stealth RO system is a customized reverse osmosis water filter that is capable of reducing up to 99% of most contaminants. It's built to give the maximum amount of flow from the membrane while sending less waste water to the drain, compared to similar RO filters. Using this type of filter will give you a clean slate to work with, enabling you to customize the nutrients being added back into your system.


  • Removes all dissolved solids from water, including chlorine and chloramine.
  • Can filter large amounts of water quickly.
  • Can remove smaller particulates other filters cannot, such as heavy metals and minerals.


  • Water going through the RO filter needs to be pre-filtered, so the membrane doesn’t clog.
  • Uses a lot of electricity.
  • Only 5 to 10 percent of the water going through the RO filter becomes usable water.

Carbon Filters

There are two types of carbon filters on the market, Activated carbon filters are the same type of filter you would see in your household drinking water filters (think Brita). The other type of carbon filter is the catalytic carbon filter. This filter does everything the activated carbon filter does, it just does it better, also making it more expensive. Having chlorine and sediment free water is essential to growing healthy plants and maintaining beneficial micro-organisms, bacteria, and fungi in your root zone and growing medium. These microbes can not survive in the presence of chlorine. Chlorine free water is also essential for organic compost tea and extraction solution brewing, hydroponics, and any bio-organic gardening method. The HydroLogic smallBoy water filter system removes up to 99% chlorine, sediment, rust, silt, volatile organic compounds (VOCs), mercury, lead, and PCBs (organic chlorine), keeping beneficial bacteria and microorganisms alive and healthy.


  • Affordable
  • Removes chloramine
  • Great when starting with a quality water source


  • Must be replaced frequently for systems that require large amounts of water
  • Does not remove everything from your water, just the larger molecules

The More You Know, The Better You Grow

It is important to know what is in the water you are giving to your plants. Most tap water is treated with chlorine and chloramine that will kill the beneficial microbes your plants need to thrive. There are a couple of types of filters on the market that will remove these compounds from your water.

The most effective for hydroponic growers is the reverse osmosis filter, as it can filter large amounts of water rather quickly. Carbon filters are better suited to those with smaller soil-based operations. Knowing what is in the water you are giving to your plants will allow you to better control the quality and yield of your grow.