A rainwater harvesting system can be a great way to make best use of this natural resource. If we disregard the importance of rainwater, our gardens will soon suffer. If you live in an area with relatively high rainfall, it is easy to forget the importance (and relative scarcity) of fresh water worldwide and of a rainwater harvesting system.
But no matter where you live, you should make sure that you are making the most of this resource. In this article, we will explore how to harvest rainwater in your garden, and the various rainwater harvesting systems you can use to store water, keep it around, and direct it to where it is needed.
Benefits of Rainwater Harvesting in Your Garden
If you grow food and garden in an arid area, where droughts are common, it is likely that you will be ahead of the curve and may already have a rainwater harvesting system. It is likely that you will already understand the importance of fresh water supply. You will probably treat it as the precious resource that it is. When something is in short supply, we tend to value it more highly.
But if you live somewhere with relatively high rainfall, you may not have had to worry about water supplies running out. In the developed world, having fresh water literally on tap means that it is not something that most of us have had to think that much about. At worst, you may have had to contend with a hose-pipe ban prohibiting the use of mains water supply to water your plants.
Having water on tap often means we forget how precious it is and ignore the importance of a rainwater harvesting system.
Rainwater Harvesting For the Environment
Water is one of our most precious resources and we are squandering it on a daily basis. As global warming and extreme weather patterns caused by greenhouse gases continue to bite, fresh water conservation will become an even more pressing concern. Many more people around the world may suddenly find themselves with serious water shortage problem.
Whether or not you yourself are personally affected by water shortage, harvesting and storing rainwater in your garden is an important step to take on the road to a more eco-friendly and sustainable way of life.
You may not realize it, but the mains water that comes piped into our homes often carries a significant cost to our planet. Water treatment plants and other facilities often require high levels of energy to run, and some also cause pollutants to enter the environment. Even when water supply is abundant where you live, the true cost of mains water supply may be high.
Rainwater Harvesting For Your Plants
What is more, drinking water from the faucet is often also filled with contaminants. Some municipalities use chlorine to kill disease-causing micro-organisms. This is bad for your plants. In areas with ‘hard water’ you may find that plants can be harmed by excessive levels of minerals like calcium and magnesium. While in some areas, drinking water will not harm plants, if you can use rainwater from rainwater harvesting systems, that will be still a far better choice for watering your plants.
Rainwater Harvesting For You & Your Household
Rainwater can also be harvested and then filtered for use in your home. Rainwater harvesting systems may cut down the costs of water where you are on a metered water supply. It could also be a more sustainable way to obtain the water you need inside your home, and could even allow you to live disconnected from a mains supply – rainwater harvesting off-grid.
How To Harvest Rainwater From Your Home
Harvesting rainwater from your home with rainwater harvesting systems is easier than you might think. It is likely that your home will already be fitted with guttering around the edge of the roof, and a downspout which will carry the water that falls on your roof down to the ground. It may then be carried away in pipes below the ground, or simply spill out onto the soil at a short distance from the wall of your property.
Rainwater collection system: Guttering and downspout on our home rainwater harvesting system.
If your home does not already have gutters, you can purchase the necessary rainwater harvesting guttering pipes from a local hardware store, or buy them online. If you do already have guttering, the hard work has already been done for you.
If you have existing guttering, but want to capture the water and incorporate into your rainwater harvesting system for use on your garden, the first step is to make sure that all the gutters are clear, and channeling water as they should with the rainwater collection system. Scoop out any leaves or other debris that is blocking the channels and preventing rainwater from flowing freely.
The next step (on a dry day) is to think about where you would like to channel the water to after it has been directed down from your roof.
Direct Water Into a Rain Barrel
Rainwater collection system: A rain barrel attached to the downspout on the house.
The easiest rainwater collection system is simply to cut off the downspout above ground level, and insert it into the top of the rain barrel, or storage tank, so water does not just go into the ground or down the drain. The water in your rain barrels can then be put to good use.
A storage tank or rain barrel which has a tap low down on its side is handy, as the rain barrel will give you easy access to the water you collect with your rainwater collection system.
You can also install a first flush diverter to prevent too much debris from entering the tank. The first flush diverter is a common feature in many rainwater harvesting systems.
Rainwater harvesting systems put to use – fill up a watering can from the rain barrels in our rainwater collection system.
Direct Water Into a Soaker Hose or Irrigation Pipes or Channels
Another rainwater collection system option is to connect the gutter pipes on your home (or the tap on a container) to a soaker hose, irrigation pipe or irrigation channel. This can direct the water that falls on your roof into a particular growing area.
Direct Water Into a Hydroponic or Aquaponic System
A third rainwater collection system option that you could consider is directing the water from your roof into a hydroponic or aquaponic food growing system. Hydroponics is the term used for growing plants with their roots in water, rather than in soil, while aquaponics is a hybrid term made up from the words aquaculture and hydroponics, and involves growing fish as well as plants. In an aquaponic system, the fish fertilise the water, which feeds the plants. There are a number of different such systems that you could consider.
Direct Water into Filtration Devices or Greywater Systems
If you want to use rainwater for your home as well as for your garden, there is also potential to direct the water from your roof into filtration devices, or to direct them into garden systems such as reed beds which allow you to deal effectively with the greywater (from sinks, baths, showers etc.) from your home.
How to Harvest Rainwater From a Shed
The same rainwater harvesting methods that are used to harvest rainwater from the roof of your home could also be used to collect rainwater from a shed, garage or other garden building. Such structures may not already be fitted with guttering and so it is likely that you will have to install it to collect water into a rain barrel.
The simple thing that you will have to remember is that water runs downhill. Guttering should be installed so that it slopes gently downwards towards the downspout that carries it down into a rain barrel or onwards to its destination.
How To Harvest Rainwater From a Plastic Greenhouse or Polytunnel
If you have a polytunnel or arch-structure plastic greenhouse in your garden, you may imagine that you cannot collect water from it. But with a little ingenuity, you can collect water from this sort of structure too and create a rainwater harvesting system out of this.
You can purchase plastic adhesive guttering – but this can often prove ineffective and unreliable. A better method involves adding a timber batten to both sides of the structure, secured using clamps to the hoops at either end. Guttering brackets are then fixed to these timber rails and used to support the same sort of guttering that you would use on a home or shed. Further timber strips are then used to close off the gap between the plastic and the guttering pipes and ensure water flows into this rainwater harvesting system effectively. The water can then be directed into a container inside or just outside the structure, or directed to flow into irrigation for the plants grown within.
Collecting and Directing Rainwater In the Soil/ Growing Areas
In addition to harvesting rainwater from man-made structures in your garden, you may also be able to collect and direct rainwater that falls on the ground into particular growing areas.
Digging on contour swales (mulch-filled ditches) can allow you to focus rainwater in particular locations, and keep it around, while irrigation channels can be used to direct heavy rainfall into holding areas, or into parts of the garden where it is most required.
Storing Rainwater in Your Garden
It is important to understand that harvesting rainwater (ie, gathering it for your use) is only the first part of the puzzle. In addition to knowing how to collect or harvest rainwater, you also need to know how to keep it around.
In order to determine how we can store rainwater in our gardens (and keep it around) it is important to have at least a basic understanding of our world’s water cycle. It is also important to understand how water flows in various ways through your particular site.
If you take a look at your garden, you will find that water is found in a range of different places. Some of the methods for storing rainwater are obvious – while others are methods that you might not have thought that much about.
In Trees & Other Plants
Trees store a lot of water and help keep it around in our woodland garden.
One of the first things to consider is that trees and other plants in your garden are themselves reservoirs of water. Each one can hold a surprising quantity of rainwater. Their roots can also help to keep water in the soil, while the shade they provide will also reduce moisture evaporation from the surrounding area. The more suitable vegetation you have in your garden, the more drought resilient it can be.
In the Soil in Your Garden
In addition to thinking about how you can keep water around in your garden through the planting you incorporate, it is also important to consider how you can improve the soil to improve its capacity for water storage. Heavy, clay soils are far better at retaining water than sandy, light and free-draining soils. You will not be able to do much about the soil type that you have in your garden.
What you can do, however, is amend and improve the soil where you live by adding mulches of organic matter, which will be incorporated into the ground by the various mechanisms of the soil ecosystem. In the past, gardeners were generally encouraged to dig organic matter into the topsoil of their growing areas. Now, however, there is a growing awareness of the benefits of ‘no dig gardening’.
In ‘no dig gardening’, soil disturbance is kept to a minimum. Rather than digging organic matter into the soil, it is simply added on the soil surface as a sheet mulch around plants. The organic matter will improve the soil’s water retention capacity. What is more, sheet mulching will also reduce the amount of water that is lost to the air.
In a Garden Pond or Reservoir
An overgrown wildlife pond in our garden.
Another more obvious way to store water from precipitation in your garden is in a garden pond or reservoir. Creating a body of water, however small, in your garden can be a wonderful idea.
Storing larger amounts of rainwater on site can be a great idea for areas where seasonal droughts are prevalent. The pond or reservoir can be an emergency back-up water supply. In areas with snow-melt or high seasonal precipitation, a reservoir can hold water from snow melt or seasonal rains for use during drier and warmer months.
A pond or reservoir can also be a good emergency measure in areas where there are increasingly frequent wildfires. In a wildfire, it could be lifesaving to have a body of water for emergency use close at hand.
Anywhere, a standing body of water in a garden can be a useful thing. It can attract wildlife that can help create a natural balance, which is great for pest control. Attracting wildlife will help to promote a healthy biodiversity on the site. This, in turn, can improve the resilience of the ecosystem and make it better able to withstand fluctuations in rainfall, temperature etc..
In Tanks, Rain Barrels or Other Containers
Of course, you can also simply store water in your garden in rainwater storage tanks, rain barrels or other containers. These can simply be fitted onto the downspouts on your home, or other water-catching set ups in your garden.
You could also consider keeping a rainwater storage tank or a rain barrel inside a covered growing area. The benefit of this is that the stored water has good thermal mass. This means that it will catch and store the sun’s heat during the day, and release it slowly when the temperatures fall at night. Improving the thermal mass in a greenhouse or polytunnel can dramatically increase the length of the growing season in temperate climate zones, and can also increase the range of crops that you are able to grow.
In an arid area, clay pot irrigation could also be something to consider. Clay pots or other small, porous vessels are used to temporarily hold water. These are buried in the soil surrounded by plants. The plant roots then draw water out through the sides of the vessels as it is needed. When filled with rainwater harvested from a collection point (or a well, or reservoir), these vessels can be a water saving way to provide edible plants with the moisture that they need.
Rainwater Harvesting – Valuing Rainfall
The rainwater harvesting tips above should help you begin to see how you can collect and store rainwater in your garden. Rather than seeing rain as a negative that prevents you from enjoying time spend outside, it is important, even in higher rainfall areas, to begin to see it as the important and valuable resource that it is.
When you master rainwater harvesting and can catch and store rainfall effectively in your garden, you can make full use of this precious resource with your rainwater harvesting system, and do your part for the planet.
Elizabeth Waddington is a smallholder, permaculture designer and environmental consultant. When not designing food producing systems or advising growers around the world, she is to be found in her own garden. On her 1/3 of an acre patch of land she has a walled forest garden orchard (home to rescue chickens), a polyculture vegetable plot, a polytunnel, wildlife pond, wild woodland garden and more and is working every day towards greater self-sufficiency. She is passionate about sustainability and loves to inspire others about the wonderful things home gardeners can do for people and planet.