It can be easy to take rainwater for granted, particularly if you live in a temperate or tropical climate where drought is a rare event. But we need to pay more attention to rainwater, because this resource, so essential to all live on earth, is not infinite. We should all be conscious of the water we use (and waste), and make efforts to maximize the functions for which water is used. This is one of the reasons why permaculture design highlights the use of mulch and cover crops to slow the rate water percolates through the soil, and suggests the use of landscape contouring and swale-building to slow the runoff of rain from the land.
Another strategy to maximize water efficiency is rainwater harvesting. This refers is the deliberate collection of rainwater from surfaces that it falls on, rather than letting the water simply run off and enter the municipal drainage system. The collected water is then stored and utilized for multiple functions in the garden and home.
Beyond the obvious benefit of capturing and using water that would otherwise go to waste, rainwater harvesting has the positive effect of reducing your water bills, easing the pressure on the municipal system of pipes, dams, wells and treatment plants, and ensuring a supply of water should extreme weather conditions affect your location. By collecting and using rainwater, you can also be assured that you have some of the cleanest, healthiest water available, as it will not have been treated with chemicals as the water that comes from your taps will have been.
If you want to use rainwater in the home, you will need to invest in filtration and pumping systems, but for use in the garden, the set-up is usually much simpler. There are several systems you can use to collect rainwater, with options suitable for both rural and urban, large and small sites.
Installing a barrel on your property is the easiest and cheapest way to begin harvesting rainwater. Place the barrel under the downspout of your guttering so that the rain that falls on the roof of your property is diverted into the barrel. Typically the container will have a spigot at the base from which you can draw water to irrigate your garden. You can affix a hose to the spigot or even connect it to a drip irrigation system. Barrels are easily sourced, either new or recycled (if going for the latter option, check what the barrel has been used for to ensure no unwanted chemical residues remain inside) and simple to install. If you live in an area where mosquitos abound, it is advisable to place a lid on your barrel to prevent the insects laying their eggs in the water, while if you live in a location that experiences freezing winter conditions, you may want to disconnect your rainwater barrel during those months to prevent it from freezing and cracking. The major downside with the barrel method of rainwater harvesting is the limited capacity, which can lead to overflowing. You should also avoid using a barrel made from translucent material; a barrel that lets in sunlight is likely to grow algae inside, which can only be got rid of by the addition of chlorine, a chemical you don’t really want to be putting on your garden beds.
It may seem odd to talk about a ‘dry’ system when discussing water capture, but this method is a recognized strategy, and so-called to differentiate it from the ‘wet’ system below. The dry system of rainwater harvesting is essentially the barrel system scaled up in size. A larger container is placed next to the property, offering a larger storage capacity than a barrel, and the guttering is diverted to the top of the tank. Like the barrel method it is reasonably cheap and easy to implement. It gets the name ‘dry’ because essentially the collection pipe ‘dries’ after each rain event, since it empties into the top of the tank. This makes it a good choice for plots in areas prone to infrequent but large storm events.
In contrast, the wet system refers to the collection pipes being constantly full of water. This is because they are underground. Multiple collection pipes are fitted to several downspouts on the property, and then run underground to the storage tank. The rainwater will rise through the pipes and spill into the tank. When it is not raining the level remains static and the pipes full. Because of the constant presence of water in the pipes, it is essential that they are watertight to prevent leakage into the soil. It is more expensive to install that the barrel or dry system, due to the underground piping, but does have the benefit that you can locate the tank anywhere on the property (as long as the inlet is at a lower elevation that the lowest gutter), unlike the previous methods that have to have it next to the building, and divert rainwater from multiple properties to one tank. With both the dry and wet systems, you need to make sure you have an adequate base on which to site your tank as, depending on capacity, they can be very heavy.
There is another method of rainwater harvesting that cuts out the middleman, so to speak. Rather than collect the rainwater in a storage unit then divert it to the garden, you could institute a green roof on your property, so that plants can utilize the water immediately. You need to put down a liner to protect your roof, and have a drainage system for excess runoff (it is most efficient if your drainage system is diverted into a barrel), but instituting garden beds planted with low-maintenance plants, means your are maximizing the productive space on your plot and making use of the rainwater where it falls. In addition, planting a green roof will also provide additional insulation to your property (and so reducing your heating bills) and protect the roof from damage.