There is nothing new about harvesting rainwater for domestic use. This practice was already widely used by our ancestors. Rain represents an inexhaustible source of soft water and it can be used in all domestic activities that do not require drinking water. This represents 50% of the water we consume around the house!
Although it is not safe to drink untreated rainwater, it can still be used in many other domestic instances: to flush the toilets, operate household appliances (washing machine, dishwasher), clean the house and the car… Your vegetable garden will also prefer rainwater to chlorinated tap water.
Rainwater harvesting systems consists of three main elements: a catchment area, generally a roof, where the rainfall is captured, a storage tank and a conveyance system, that channels and filters the water in and out of the tank.
Prepare the rainwater catchment area
A roof represents the ideal water collection area for a house: the larger the collection area, the more rainwater can be collected! Keep in mind that roofing materials can impact rainwater quantity and quality. For instance, non-absorptive roofing materials, such as steel, are best suited to rainwater collecting. On the other hand, the amount harvested during a rainfall can be reduced by porous materials such as wood shingles or clay and concrete tiles, which have a tendency to soak up water. Keep in mind that when rainwater runs over the roof surface, it may absorb potential contaminants such as heavy metals and pesticides. Animal droppings, leaf litter and dust on rooftops can also pose a health risk if they are washed into the rainwater system. It is therefore essential to keep your roof clean and design a system that discharges the first few liters of rain into the garden until the roof is clean.
Compare rainwater storage options
When choosing the size and design of your rainwater tank consider several elements: rainwater supply, catchment surface area, aesthetics, personal preference, needs and budget.
Depending the available space, rainwater can be stored in underground or aboveground storage units. Polyethylene or polypropylene tanks are most commonly used. Lightweight and durable, they come in various shapes and sizes. They are typically suited for both aboveground and underground installations.
- Underground tanks
If you are prepared to excavate your garden with a mini-digger, opt for an underground model: the water will be stored away from light, heat changes and bacteriological contamination. Rainwater will therefore not turn green or malodorous. Cast as part of a building’s foundation or installed separately elsewhere on your property, the main advantage of this option is that the tank and most of the conveyance system remain invisible. The overall system remains relatively simple and requires little maintenance. However, greater care is essential in its initial design. Also, as cars and plantations are not allowed above the tank, a large outdoor space is a prerequisite for this type of installation.
- Aboveground tanks
Less expensive to install and maintain, aboveground tanks represent great value for money. The ideal is to place the rainwater collector in the shade. On the down-side, they are subject to sunlight and other weather conditions, such as freezing, that can affect the system. In addition, they can take up a lot of residential space and may not be considered visually attractive to some. Yet, with the growing popularity of rainwater harvesting, more aesthetically-pleasing models are being introduced, presenting a variety of pleasing colors and configurations. Additional materials specific to aboveground installations also include galvanized steel, stainless steel and wood.
Optimize conveyance systems
A conveyance system consists of gutters or pipes that deliver rainwater to a nearby storage tank. Drainpipes should be constructed of chemically inert materials such as plastic, aluminum, fiberglass or wood in order to avoid adverse effects on water quality.
Once the rainwater is stored, it can be supplied to appliances throughout the house either with a direct pump system that pumps water directly to the point of use when required, or a gravity fed system, which pipes rainwater to a header storage tank, usually in the loft, and delivers it to appliances using gravity.
Pre-filtration devices are usually incorporated to the conveyance system in order to prevent solid debris and leaves from entering the storage tank. While no further treatment is actually required for the domestic use of non-potable rainwater, a certain number of guidelines are recommended to maintain the quality of the water. For instance, the installation of overflow siphons, which allow for floating materials to be removed and rodent barriers, to prevent small animals from entering the tank.