Which Water For Hydroponics? [Explaining the Different Water Types]

The success of a hydroponics system depends largely on the type of water you use. So, which one is the best?

Mineral water, tap water, purified water, and distilled water are all viable options to use for hydroponics because they are safe for human consumption and are proven to not harm plants. Distilled water has the lowest TDS level of ~1 ppm, making it the best option to use for hydroponics. Wastewater and rainwater cannot be used in hydroponics unless treated.

If you are wondering why some types of water may be better for hydroponics than others, let me explain the factors that make each water type suitable for hydroponics.

Role of Water in Hydroponics

Water acts as the controlled solvent in hydroponics and the growing medium used to replace soil. Water serves as nutrient transport, nutrient holder, oxygen delivery system, and as a component for photosynthesis.

Ordinarily, water serves the role of nutrient transport inside the plant body. The water inside the plant carries nutrients to and fro the different plant parts much like how blood in the human circulatory system.

In hydroponics, water in the nutrient reservoir is modified so that it carries nutrients such as nitrogen, phosphorus, and potassium, and oxygen through the use of the reservoir and air pumps. This modification allows it to hold nutrients like soil but without drowning the plants due to the dissolved oxygen in the water.

The Importance of Water Type in Hydroponics

The total dissolved solids (TDS) level of water has a direct relation to the electric conductivity (EC) and acidity (pH) of the water. The higher the TDS, the higher the EC, and the more acidic the water is (pH < 7). The ideal conditions for the nutrient solution in the reservoir are ~800 TDS, ~1.2-2 EC, and 5-6.5 pH.

Hydroponics thrive on controlled conditions specifically adjusted by the gardener or grower for ideal growing. Water types with lower ~1 ppm are more conducive to ideal growing conditions.

Some gardeners or growers may want a lower TDS level from their water source to have a completely sterile and controlled solution in their systems. This is especially important since some are unfortunate enough to have water that has a TDS 500-1000 ppm courtesy of their water utilities provider.

Types of Water Usable in Hydroponics

Water with a maximum TDS (total dissolved solids) lower than 500 ppm (parts per million) will be reasonably clean and usable for hydroponics. From most to least in TDS level, there are: 1) tap water, 2) mineral water 3) purified water, and 4) distilled water.

Generally, most water types are usable in hydroponics, with lower TDS levels being more effective. If plants can survive and evolve for millions of years taking less than optimal water, then it can definitely take water that’s perfectly safe and usable for humans.

1. Tap Water

Tap water is often suitable for hydroponics. In the United States, it has an average TDS (total dissolved solids) of 350 ppm (part per million), making them safe for humans and plants.

Tap water comes out of faucets and is often supplied directly by local water utilities. Tap water is generally clean and usable for most purposes because of the chlorine and filtration treatment applied to it. However, some places may have tap water that has a TDS content of above 500 ppm which can be a cause for concern.

Note: If you’re unsure of the quality of your local tap water, an easy and efficient method to lower the TDS level is by attaching an activated carbon filter. Water is physically strained through the activated carbon filter, resulting in purer water output.

2. Mineral Water

Mineral water is a suitable choice of water for hydroponics. According to US law, it has at least a TDS of 250 ppm, making it reasonably safe for humans and plants.

Mineral water is sourced from naturally underground wells or springs. It is perceived by the public as a healthier and cleaner alternative to tap water because of its naturally occurring origins and general lack of chemical treatments. However, this means that mineral salts or microbes may still be present in the water.

Note: Mineral water with a high TDS level can be purified by filtration, reverse osmosis, ozonization, or distillation. The easiest and most cost-efficient method is through filtration wherein water is sieved through activated carbon filters. A purer yet more costly method is distillation which requires boiling the water and collecting the purified condensed steam.

3. Purified Water

Purified water is potentially one of the best water choices for hydroponics with a TDS level of less than 10 ppm. Purified water undergoes reverse osmosis or ozonization, resulting in the removal of microbes, chemicals, and mineral salts and so limiting problems in hydroponics.

Reverse osmosis operates by forcing the untreated water through a semi-permeable membrane that separates the water from the unwanted contaminants, mineral salts, or microbes.

Ozonization is an advanced oxidation process that operates by using ozone (O3) to remove microbes and other impurities in the water. Ozonization is more expensive and not as common as other methods.

4. Distilled Water

Distilled water is possibly the purest form of water and the best choice for hydroponics with a TDS level of ~1 ppm. Distilled water is a type of purified water that has undergone distillation that results in mineral salts and organic matter being completely removed.

Distillation works by boiling water until it evaporates and then collecting the steam condensed steam. The boiling process kills microbes and evaporates contaminants and the evaporation makes sure that mineral salts or other particulate matter are separated.

Water Types Not Usable in Hydroponics

Wastewater and rainwater are not usable in hydroponics. Wastewater is full of microbes and human waste whereas rainwater often has traces of contaminants from catchment surfaces.

These water types, without further treatment, will not provide a clean or usable water supply for any hydroponics system. They will introduce pathogens, microbial growth, and nutrient imbalance in the system. This leads to degradation in plant health and eventually death.

1. Wastewater

Wastewater refers to water used in homes, businesses, or industries and carried by sewage systems. Wastewater is unsuitable for hydroponics due to how impure and contaminated it is.

Wastewater can be treated however such a process is too costly for the purposes of hydroponics. It might be more cost-effective to use fresh tap water to refill a system than trying to recycle wastewater.

2. Rainwater

Rainwater comes from natural rain, funneled from catchment surfaces, and stored for use. It is not suitable for hydroponics due to possibly being contaminated with microbes, small insects, pollution particles, or chemicals.

Several studies have already reported that stored rainwater fails to meet WHO standards on water drinking safety. Stored rainwater is a good site for microbial contamination or pests infestation. Apart from that, rainwater can be further contaminated due to atmospheric pollution and trace chemicals (i.e. zinc or lead) from catchment surfaces such as roofs or walls.

Water Purification Methods

Water purification methods come in all price points and sizes – from residential to industrial use. Even the cheapest ones can significantly improve the purity of the water, making the water more suitable for hydroponics.

These can be as simple as using activated carbon or as complex as using a reverse osmosis machine. Current water purification methods are now affordable, commercialized, and available for home use and do not require much investment in terms of finances or space.

More advanced water purification products can even make wastewater and rainwater drinkable therefore usable for hydroponics.

The Handy TDS/EC and pH Water Tester

The water testers are an essential tool for any hydroponics system. They accurately measure the TDS, EC, and pH of the water in the system, allowing the gardener to adjust accordingly whenever the conditions are not ideal.

The water testers are the unsung hero of hydroponics since they are the first thing to tell you what’s wrong with your system. They are simple to use and intuitive, providing data almost instantly. Furthermore, they are multipurpose. You can use them for your drinking water, your aquarium water, and your hydroponics system.

Summary of Which Water For Hydroponics

Mineral water, tap water, purified water, and distilled water are all viable options to use for hydroponics. Though a lower TDS level is preferable, water with a TDS level not greater than 500 ppm is usable for hydroponics. Distilled water has a TDS level of ~1 ppm, making it the best option to use for hydroponics.

If water is good enough for human consumption, it is good enough for hydroponic use. However, wastewater and rainwater are unusable for either hydroponics or human consumption. Wastewater is full of microbes and human waste while rainwater has traces of contaminants from catchment surfaces.

Water purification methods are now commonplace, allowing gardeners to provide cleaner water to their systems at an affordable price and at varying scales.

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