If you can afford to, installing a rainwater tank is a good idea not just for permaculturists (although it does correspond very neatly with permaculture’s focus on recycling resources and trying to maximize the number of functions they perform) but also for everyone. They are particularly useful in areas that experience periods of low rainfall and high temperatures, as they can store water from previous rainy seasons for use as irrigation when the climate does not provide for the garden. Indeed, in one such country, Australia, the installation of rainwater tanks is becoming more and more popular, with more than a quarter of homeowners now having one on their property. There are even some locations – often those prone to drought in the summer – where new homes being built must include a rainwater tank mandatorily.
Rainwater tanks harvest the rainwater that falls on a property’s roof, diverting the flow from the guttering into a tank, rather than allowing it to enter the drain. The stored water can be used to irrigate your plot, but can also be utilized in flushing the toilet and running laundry appliances. Because the water captured in the tanks if free, you will save on water bills, as well as avoiding wasting water. Other beneficial impacts of harvesting rainwater include less cost to the community of maintaining and updating pipes, dams and treatment plants to supply municipal water; reduces damage to habitats from storm water runoff, particularly in urban areas where there are a lot of impermeable surfaces; and the water has not been treated with chemicals, as the municipal supply has.
If you are considering installing a rainwater tank on your site, there are a number of things to take into account. The size of your property will be important, as will the amount of rainfall you receive in your location, the size of the roof from which you will be harvesting the water, and the uses you wish to put the rainwater to. Another consideration is the material the tank is made from. Your choice will be linked to other factors, such as space and use, but different materials also have different properties that will affect your decision.
The weight of concrete tanks means that they are primarily installed underground. This can be useful in order to save space in the garden, but will obviously require significant excavation in the first instance, which has the added effect of making them the most expensive type of tank to install. Concrete tanks are more likely to be subject to planning restrictions than other, more lightweight aboveground tanks. If you install a concrete tank, be aware that lime from the concrete can leach into the water, particularly in new tanks. This can turn the water alkaline, which is not good for most plants. Using a lining for your concrete tank can avoid this.
Metal tanks have always been the traditional alternative to a concrete tank, being an aboveground tank, cheaper than concrete, and lighter so easier to install. Originally metal tanks were fabricated from galvanized steel – meaning steel sheets were covered with a coating of zinc – which allowed the steel to be soldered together, meaning tanks could be manufactured in different shapes and sizes. The problem with galvanized steel is that they are prone to rust, particularly if they are used with copper or brass fittings and pipes. The rust from inside the tank that gets in the water, is not harmful to plants (at least not unless it is in very large quantities), but the rusting associated with galvanized steel tanks will eventually undermine the integrity of the tank, causing leaks and necessitating a replacement. These days, manufacturers are using other metals, such as aluminum to try and prevent rusting.
One material that some rainwater tanks are made from that doesn’t rust is fiberglass. Fiberglass is a polymer of densely woven strands of plastic that has been reinforced by glass fibers. This reinforcement means that fiberglass is very string. Indeed, tanks made from fiberglass are stronger than most metals. This makes them a good choice if you want a large tank with a big capacity, as the tensile strength of the material can withstand the pressure of a large amount of water. However, fiberglass tanks tend to be more expensive than other plastic-based tanks, such as those made from polyethylene.
The low cost of polyethylene is one of the reasons why it is currently among the most popular choices of material for rainwater tanks. They are also very lightweight and so easy to transport and install. They may experience some corrosion if exposed to high levels of sunlight, but not for many years. Because they are manufactured by being molded around a central steel mold, they tend to come in standard shapes – usually circular – and sizes (as manufacturers do not want the expense of creating an individual mold for each client). This can be a downside if you have an irregular space in which to site your tank.
If you do have an irregular space, or a small space, for your tank, one option is to install a rainwater bladder. These are made from a flexible membrane that expands when water enters the bladder, and contracts when liquid is siphoned off. Typically, rainwater bladders are installed in a rudimentary frame to prevent movement, and can be installed in the crawl space underneath your property if you don’t have space in the garden (although this may require some pipe work to divert the feed from the guttering under the house). They can also be used vertically, so can be placed in a frame against a fence or wall. Bladders are, literally, the most flexible option for your rainwater tank, but do have the drawback of the most limited capacity of all the options. However, if you have a small plot, you water needs will be less than larger locations, and bladders may also be a viable option if you want to use rainwater for household water needs and your dwelling is small or you household is few in number.