Unlike soil-based gardening, hydroponic gardening involves growing plants in a nutrient solution. The water used for hydroponic systems can come from tap water, distilled water, and well water. But can you use rainwater for hydroponics?
It is safe to use water collected from rain barrels in your hydroponic system. Unlike tap water, rainwater does not contain added chlorine or chloramines. In addition, rainwater does not contain as many dissolved minerals as tap water. Finally, rainwater is slightly acidic which makes it well-suited for plant growth.
To collect rainwater, hydroponic gardeners can install a simple rainwater harvesting system.
What is Rainwater Harvesting?
Rainwater harvesting involves collecting rainwater from an impervious surface such as a roof or gutter and storing it for later use. Rainwater harvesting is often referred to as rainwater collection.
The water from rainwater harvesting systems is used for a variety of uses including watering plants, flushing toilets, and even water supply in some cases. I do not recommend that you drink water from a DIY rainwater harvesting system unless you are 100% sure you know what you are doing.
Benefits of Rainwater Harvesting
There are a number of benefits to rainwater harvesting. Some of these benefits are listed below:
- Good for the environment – Do you need potable water for your lawn or garden? No! By using rainwater harvesting for non-drinking purposes, gardeners are participating in more sustainable practices and helping the environment. In addition, rainwater harvesting will minimize the soil erosion near your downspouts.
- No chlorine or chloramines added like water delivered by municipalities. This means you do not have to worry about these chemicals harming your plants if you use collected rainwater for gardening or hydroponics.
- Reduces the water bill – Because you are using water that falls from the sky rather than the tap, you are essentially collecting free water! That means you can save a little bit of money using the water from rainwater harvesting for non-drinking purposes.
- Lower pH – Rainwater has a pH of about 5.6. This is good news for hydroponic gardeners whose drinking water has a higher pH (mine is consistently around 8.2).
Is It Okay to Use Rainwater for Hydroponics?
It is definitely okay to use rainwater for your hydroponics systems, but the water will probably need to be treated. Because rainwater flows off of impervious surfaces such as roofs and gutters, it will contain some contaminants.
The quality of the water obtained from a rainwater harvesting system is directly related to the cleanliness of the rooftop and storage tank. Dust, bird droppings, and leaves tend to accumulate on rooftop surfaces. These contaminants can enter your rainwater collection system if you do not install a pre-treatment system such as a first-flush diverter or sediment trap.
The contaminants present in rainwater also depend on how often it rains in your area. If it rains infrequently, there is more time between rain events for sediment and other contaminants to build up. Therefore, the rainwater will contain more contaminants.
Studies have shown that rainwater collected in storage tanks tends to have a pH of around 5.6 which is on the lower side of the pH range that is acceptable for hydroponics (5.5-6.5).
Local Laws
Before you invest in a rainwater collection system, check your local regulations to make sure rainwater harvesting is legal in your jurisdiction.
You may be wondering why rainwater collection is illegal in some places. The answer lies in how the western states have historically handled water rights. In the mid-1800s, many western states were operating under the doctrine of prior appropriation. This means that the water that falls on your land is not necessarily your water. That water has already been allocated to another “beneficial use.”
States have been lightening up on the restrictions associated with rainwater harvesting. In 2012, the State of California passed a law that made it legal for residents to collect water that runs off their roof. Under House Bill 16-1005, the State of Colorado made it legal for residents to install a maximum of two rain barrels on their residential property.
Setting Up a Rainwater Harvesting System for Hydroponics
Now that you understand what rainwater harvesting is and how the water can be used for hydroponics, it is important to understand the components of a rainwater harvesting system.
Many homeowners and gardeners only need a rain barrel to capture the rainwater required for their hydroponic systems and soil gardens. The rain barrels available online and at places like Home Depot often include all of the components listed below.
However, it is still a good idea to understand each component so you can upgrade your system if required.
One of the great things about rainwater harvesting is that it is really easy to customize your system. This means that you can build a system that really fits your needs.
Catchment Surface
People typically collect rainwater from their roof or gutter. Using your roof or gutter as a catchment surface is probably the simplest and most effective way for home gardeners to set up their rainwater collection system.
However, there are rainwater harvesting systems available that may make it possible to collect rainwater from your deck or patio.
Storage Tank
The storage tank is the component of the rainwater harvesting system that will actually collect water. Storage tanks are also called cisterns. There are a few things to consider when selecting a storage tank.
First, determine the size of the storage tank that you need. Most homeowners and gardeners will only need rain barrels rather than large cisterns. Rain barrels are typically much less expensive than larger rainwater harvesting systems and are constructed from 55-gallon containers.
Then consider the material used to construct your storage tank. Storage tanks are typically made of plastic or metal. Plastic is less expensive, but many people like the aesthetics of a metal tank. It is important to note that special materials are required if you are going to store drinking water in your rainwater harvesting system.
Terracotta and charcoal stone rain barrels are also available online.
Finally, it is important to purchase a storage tank that is darker in color. Translucent or light colors may promote algal growth inside of the storage tank.
Pre-Treatment
The purpose of a pre-treatment system is to clean the rainwater as much as possible before it flows into the storage tank. Keep in mind that your system could contain more than one pre-treatment device.
First Flush Diversion System
The “first flush” of a rain event contains the highest levels of contaminants because it is washing away the sediment and bird feces that have built up on the catchment since the last rain event. After the initial rainfall has carried away this contaminant buildup, the concentration of contaminants in the rainwater will decrease.
To avoid the high levels of contamination associated with the first flush, it is a good idea to install a system that will divert the first six or seven gallons away from the storage tank. Diverting the first flush will also minimize the amount of sediment that accumulates in your storage tank.
There are first flush diverters available for purchase that will automatically divert a specified amount of water. After that, water will flow slowly into the rainwater collection system.
It is important that you select the correct size for your first flush diverter. If you select one that is too large, you will diminish the amount of rainwater you can collect. On the other hand, a first flush diverter that is too small could overflow, and sediment will enter your system anyway.
Sediment Trap
A simpler alternative to a first flush diverter is a sediment trap. A sediment trap contains a removable filter that separates water from sand. The sand will settle to the bottom of the tank.
Sediment traps do not require as much maintenance as a first flush diverter and are simpler to incorporate into your system.
Debris Filters
There are also a variety of filters available to capture large debris before the rainwater enters the storage tank. These filters could be as simple as a wire mesh cover or as complex as a vortex filter.
Tank Screen Cover
Uncovered storage tanks can also attract mosquitos. In addition, exposing the water to sunlight can promote algal growth. Covering your storage tank is essential for maintaining an acceptable level of water quality in your storage tank.
Overflow
Some type of overflow or bypass system is required so that water has somewhere to go once the storage tank is full. The overflow should be located at the top of the storage tank.
Distribution System
Your distribution system is the mechanism used to obtain water from the storage tank. Your distribution system can be as simple as a spigot or a couple of feet of hose with an on/off value.
If you are going to rely on gravity by using one of the distribution systems mentioned above, it is important that you elevate your tank.
If you are going to install a very large tank or convey water across your yard, it might be worth installing a small pump.
System Cost
The cost of a rain barrel depends on the size of the barrel as well as the material used to construct the system. You can expect to pay between $100 and $200 for a decent 50 to 60-gallon rainwater collection system.
Maintenance
With proper maintenance, your rainwater harvesting system will provide high-quality water for several years.
- Clean sediment traps every couple of months.
- Clear leaves and other debris from your gutters.
- Check that none of your filters are damaged. Maintain all filters per the manufacturer’s recommendations.
- Inspect your tank for signs of algae growth.
- Drain and scrub your rain barrel annually.
