It is generally known that hydroponics use less water than conventional farming methods; but the question that most people often ask is how much water does hydroponics use? Most people want to know the specifics of any endeavor before making a decision. This is understandable since what may be considered less can be very subjective and water is actually not free. You have to pay for it irrespective of your water source (municipal supply or private sources – borehole, well, etc.)

What is the Minimum Water Requirements for Hydroponics

It can also be a little challenging to decide specific amount of water that will be needed for hydroponics since various factors are involved. However, there is a general rule that can be used for estimating minimum hydroponic water requirements.

Plant Size	Amount Per Plant
Small Plants	0.5 Gallon (1.89 Liters)
Medium Plants	1 – 1.5 Gallons
Large Plants	2.5 Gallons

These recommended estimates are the required minimum amount of water needed for hydroponic plants which is based on the plant size. 

Small sized plants need about half gallon of water, medium sized plants will need between 1 – 1.5 gallons of water, and large plants need about 2.5 gallons of water.

What Factors Affect Water Uptake in Hydroponic Plants

Obviously, as the plants grow, their water uptake may increase considerably and this may require more water to be provided. However, besides the increase in plant water uptake, there are also other important factors that may affect water availability for hydroponic plants. These include:

Temperature: In this case, this is basically a measure of how cold or how hot the environment or air around the hydroponic plant is. High temperatures typically make plants to transpire the more through a process known as transpiration which helps plants to cool down during high temperatures. The water that is lost as a result of transpiration is then replaced by the plant roots taking up more water from the reservoir.

When the temperature is low, the rate of transpiration is low and the rate of water loss through transpiration is also low. This makes the uptake of water by the plant roots become slow as well.

Hence, this can significantly affect the amount of water that the hydroponic plant needs.

Humidity: Humidity can be described as the amount of water vapor in the air. Humidity is said to be high when the amount of water vapor in the air is high or more than 50%. Alternatively, low humidity tends to occur when the amount of water vapor in the air is less than 30%.  

Plants generally tend to transpire more and lose water from transpiration when the humidity is low and they tend to transpire less (and lose less water) when the humidity is high. Hence, water uptake by the roots of hydroponic plants will be more in low humid environments because of the need to quickly replace water that is lost from transpiration. Conversely, water uptake will be less in high humid environments since the rate of transpiration is low, there will be less need for replacing water in the plant.

Wind: Wind also play a significant role in the uptake of water by plants. Wind may enhance the rate of transpiration by making water to evaporate at a faster rate from plant surfaces (leaves, stems etc.). This can contribute to higher rates of transpiration especially in a low humid hot weather. The uptake of water by plants will likely be at the same rate as the loss of water. Hence, wind should also be a factor when considering the quantity of water that will be needed for your hydroponic garden.   

Light: Light is a requirement for plants to produce their own food or carryout their own metabolism, a process known as photosynthesis. Water is one of the raw materials that is needed for photosynthesis to happen and light must be present for this to happen. Hence, it is easy to understand that the rate of water uptake by the plants will be higher during daylight hours. The rate of water uptake will also likely increase or be higher during seasons with longer daylight hours than during seasons with short daylight hours since the process of photosynthesis will be ongoing during daylight hours.

How Often Should You Water Hydroponic Plants

Typically, plants should be water 2- 3 times a day and this frequency can be changed as plants grow and become mature, but more importantly how often should you fill or change water in your hydroponic reservoir? The best answer is – it depends on the rate of water uptake by your hydroponic plants. Here is the thing, you don’t want to keep changing in a fixed frequency except if you cannot measure the PH of the water or the nutrient concentration in the water.

Typically, as plants take up water from the reservoir, water may be absorbed faster than the nutrients in the solution, which alters the PH of the water. Water with a high or low PH will definitely hurt plants but when you can measure your water PH all the time, it will help you to make adjustments and know when to add water, and how much water to add or when to change the entire solution completely.

However, if you do not have any way of measuring these indices (water PH, nutrient concentration etc.), then it may be logical to change the water periodically. But this may not be the best way of managing the water levels in your hydroponic reservoir.

Considerations for Maintaining Optimal Water Volume

The main key to maintaining optimal water volume for your hydroponic reservoir is to understand the factors that influence water uptake by plants and water loss from the reservoir. Some of these factors include:

Leaks: It is very important to ensure that your hydroponic reservoir does not have any leaks. Unidentified leaks may result in misleading information about water uptake and utilization by plants. Operating a container or reservoir without leaks helps you gives you accurate information which can help you to understand the system better.

Evaporation/Greenhouse: Another factor that is important in maintaining optimal water volume for hydroponic plants is evaporation. Water from the hydroponic reservoir can be lost from evaporation if it is not properly covered or shielded from the environment. Hydroponic plants grown under a greenhouse tent environment are less likely to be exposed to evaporation since greenhouse tents protect them from environmental influences like sunlight, wind, humidity, etc. which tend to affect the rate of water loss.

Nutrient Concentration/PH: An imbalance occurs when water loss or uptake occurs at a faster rate than nutrient uptake. This makes the hydroponic solution become concentrated with the PH becoming higher or lower (alkaline or acidic). Any of these resulting extremes of PH can be detrimental for the plants, and the best thing to do may be to add water and restore that balance to a neutral PH or change the water completely if this cannot be done.

Conclusion

How much water that hydroponics use depends on several factors that influence the rate of water uptake by plants and the direct loss of water from the hydroponics reservoir. A good understanding of these factors will help you determine the amount of water needed for your hydroponic plants at any time.