All About Large-Scale Rainwater Collection

Learn the basics of large-scale rainwater collection systems and compare the pros and cons of underground versus above-ground tanks.


©2007 Dorling Kindersley Limited

2007 Dorling Kindersley Limited


Domestic systems on a large scale involve the use of large storage tanks, which may be above ground but are more commonly buried underground (see image above). The advantage of a subterranean tank is that it saves space, is more aesthetically pleasing, and is shielded from direct sunlight so that the water maintains a more constant temperature (meaning there is less likelihood of algae growth or bacterial build up). Correct placing of the tank requires careful planning, as you may need to adjust gutters and downpipes to maximize the amount of water delivered to the tank.

How Does the Tank Work?

Water enters the tank through a "calmed inlet," which means that sediment at the bottom of the tank and residue on the surface of the water is not stirred up. Once collected, the rainwater is pumped back into the house. The pump may be located in the tank itself, which reduces noise but is less accessible for maintenance. Conversely, you can site a suction pump inside the house, which is more accessible but may prove noisy.

Topping Up Water Levels

When the tank level is low, plumbed-in water is used to top it up so that the tank does not run dry. With this type of system, it is important to ensure that there is an air gap between the rainwater supply and the top-up supply to prevent contamination. This can also be achieved by non-return valves-check with your local authority regarding regulations. Similarly, the overflow from the tank to the water drains must not allow any backflow of material. Monitoring systems may also be purchased and installed as part of a large-scale rainwater tank system.

Maintenance and Treatment

The only significant maintenance required for a rainwater tank is to ensure that filters are regularly cleaned and gutters and downpipes are unblocked. Be aware that there are moving parts in this system, such as pumps and valves, which may need occasional servicing. Some domestic systems use UV filtration to make the water drinkable, although this does require more advanced hardware.

Tank Size

Consider the size of tank you require before installation. Typical domestic sizes range from 1,320 to 2,640 gallons. You can make a more precise estimate by calculating the roof size of your home, balanced against the annual rainfall in your area, in relation to your estimated water consumption. Most suppliers will help you with this calculation before you order.

Underground or Above Ground?

With large rainwater collection systems, it is most common to situate tanks underground. However, the expense of this option means it may be worth considering a surface collection tank. It is also easier to identify leaks, or other problems, in an above-ground tank. A disadvantage with this system, however, is that water can overheat and become a host environment for algae and bacterial growth. In addition to this, large tanks can also be an unattractive feature in your yard, although a range of designs is available to cater to specific space and positioning requirements.

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