What are the different types of rainwater harvesting tank?
Once you’ve made the decision to invest in a rainwater harvesting tank, you then need to settle on the type of system you want to install. Here we look at the shallow dig and aboveground models, two of the most popular types of rainwater harvesting systems around.
A shallow dig rainwater harvesting system is exactly as it sounds – a low profile tank that has a slim line design that does not require you to excavate too far into the ground. This can be particularly helpful for gardens that have wet or rocky ground that will make it difficult to dig down too far. A shallow dig system may also be your only option if have a narrow side passage along the side of your home, which will make it impossible for get machinery on-site.
Most underground tanks have a capacity somewhere between 1,000 to 6,000 litres, although it can sometimes be more for larger properties. Of course, a shallow dig system will be at the lower end of this scale, as the slimmer profile means there is a limit on how much capacity it has available.
The hole for a shallow dig tank will be around one metre deep, compared to a few more metres or more for a larger tank. You should be able to excavate using a shovel instead of hiring a digger to make a large enough hole.
Some regions have higher water tables than others, which means you do not have to dig down too far to locate saturated soil. A shallow dig water harvesting system is a good fit for this as there is less underground water to pump away while it is being installed. It also means there is less chance of the tank floating up and breaking through the surface once work has been completed.
You’ll find aboveground rainwater harvesting tanks available in a variety of styles and sizes, including simple barrel designs to more decorative models that are intended to mimic outdoor features so they blend in more easily.
The installation process is easier than a belowground model, as you only need a firm level base and enough space. From there you connect a few components to the downpipe and the system is ready to receive rainwater from the roof. For a small garden, an above ground system will usually hold a few hundred litres, which should be more than enough for watering the garden, washing down the driveway and similar household tasks.
One thing to be aware of with aboveground tanks is that they should either be insulated or drained down during winter. This is because the water could freeze in very low temperatures, which can lead to the pump or other components being damaged. Adding insulation is easy and cheap to do and you should also ensure the connected pipework is also insulated.
Things to consider before installing an underground rainwater harvesting tank
Check below the surface
Before installation begins, you should get a better understanding of what lies beneath the ground in the area you want to position the tank. If underground utility pipes and other access restrictions are in place, a shallow dig may be your only option. For a deep dig tank, you may want to look at ways of avoiding damage being caused to pathways or other areas of the garden that can be caused by heavy plant machinery.
You also need to plan how surplus soil will be removed from the site after work has finished. For a shallow dig installation, the hole is smaller, so the amount of excess soil will be far less. It takes time to remove earth and it’s a job that should ideally be done by professionals – so this is a cost implication that needs to be factored into your total budget. Also make plans for where the earth will be placed while it’s awaiting collection as it can cause some disruption if you are unprepared.
There are some health and safety implications to consider too. If you are installing a larger tank, there should be sufficient support in the sides of your trench. The Health & Safety Executive do not state the depth at which a trench needs to be supported in terms of safety, but they do say you should consider weather and ground conditions and nearby work activities, regardless of the trench depth. Guidelines on the trench depth should be provided by the product provider or taken care of by the installation company.
While maintenance requirements for underground tanks are very low, repairs or maintenance may need to be carried out at a later date. A shallow dig tank will be easier to access than a deep dig installation for this reason, which less chance of any damage being caused. Plant machinery may have to be used to access a deep dig tank, depending on the type of work that needs to be carried out.
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