What type of tank is used for rainwater harvesting?
The type of tank used for rainwater harvesting depends on your available space, budget, aesthetic preferences, and intended use. There are several common tank types, each with advantages and disadvantages.
Polyethylene (Plastic) Tanks
Polyethylene tanks are the most popular choice for domestic rainwater harvesting. They are lightweight, durable, UV-stabilised, and available in a wide range of sizes from 100 to 10,000 litres. They are relatively inexpensive, easy to install, and resistant to corrosion. Polyethylene tanks should be opaque to prevent algae growth. They come in various colours and can be shaped to fit against walls or in corners. The main disadvantage is that they can become brittle over time with prolonged UV exposure, though UV-stabilised grades last many years.
Concrete Tanks
Concrete tanks are extremely durable and long-lasting, with a lifespan of 50 years or more. They are typically used for underground installations or larger systems. Concrete provides excellent thermal insulation, keeping water cool in summer. The mass of concrete prevents the tank from floating when empty in high water table conditions. However, concrete tanks are heavy, expensive, and difficult to install. They require professional construction or installation. Over time, concrete can leach calcium into the water, slightly increasing hardness, though this is rarely significant.
Fibreglass Tanks
Fibreglass (GRP) tanks are strong, lightweight, and resistant to corrosion and UV damage. They can be moulded into complex shapes and are available in sizes up to 50,000 litres. Fibreglass is an excellent choice for underground installations because it is strong enough to withstand soil pressure. The smooth interior surface resists algal growth and is easy to clean. Fibreglass tanks are more expensive than polyethylene but offer greater durability and design flexibility.
Galvanised Steel Tanks
Galvanised steel tanks are robust and have a distinctive appearance that some people find attractive. They are suitable for above-ground installation and are available in large sizes. Steel tanks are fire-resistant and very strong. However, they can rust if the galvanised coating is damaged, and they are more susceptible to denting than plastic tanks. In hard water areas, mineral deposits can form on the interior surfaces. Steel tanks conduct heat more readily than plastic or concrete, which can promote algae growth in hot weather.
Above-Ground vs Underground Tanks
The choice between above-ground and underground installation is one of the most important decisions. Above-ground tanks are less expensive to install, easier to access for maintenance, and simpler to connect to downpipes. They are available in a wider range of sizes and shapes and can be moved if needed. However, they take up garden space, are visible, and are more exposed to temperature extremes. Underground tanks save space, preserve aesthetics, keep water cooler in summer, and protect water from freezing in winter. They are more expensive to install due to excavation costs, harder to access for maintenance, and require careful consideration of groundwater, soil conditions, and overlying uses. For most domestic installations, above-ground tanks are the most practical and cost-effective option. Underground tanks become more attractive when space is limited, visual impact is a concern, or winter operation is essential.
Tank Accessories and Features
Modern rainwater tanks come with a range of accessories that enhance functionality. Calming inlets reduce turbulence when water enters the tank, preventing disturbance of sediment at the bottom. Floating intake filters draw water from below the surface where it is cleanest, avoiding floating debris and settled sediment. Overflow siphons create a water seal that prevents mosquitoes and odours from entering through the overflow. Inspection hatches allow access for cleaning and maintenance. Tank connectors allow multiple tanks to be linked together for increased capacity. Submersible pump kits include all necessary fittings for pressurised water supply. Many manufacturers offer comprehensive accessory packages that simplify system design and ensure component compatibility. When purchasing a tank, consider which accessories you will need and whether they are included or available as options.