How Do I Plan For A Rainwater Harvesting System?

If you’ve already decided that you want to install a rainwater harvesting system, there are a few other practicalities to get out of the way to make sure everything goes smoothly. This FAQ by Owls Hall Environmental gives you information on the key things to consider.

Can you get a grant for a rainwater harvesting system?

Unfortunately, there are currently no grants available for Rainwater Harvesting systems. We have a range of systems to suit all budgets from simple water butts to small garden watering systems.

Given the increase in demand for drinking water in the UK, we encourage all homeowners to be conscious of their water usage. You can save water without spending a penny by reading our tips on water saving.

Do I need planning permission to install a rainwater harvesting system?

No, you do not require planning permission to install a rainwater harvesting system.

Although it is often viewed in a positive light by planners and may help to gain planning permission for a new home if you install a rainwater harvesting system.

Can a builder install a rainwater harvesting system?

Yes, a competent builder or ground worker can install our rainwater harvesting systems. All our systems come with instructions to guide you through the installation process. A plumber will be involved as will an electrician. We have first class technical support to help over the phone too.

What additional plumbing do I need for a rainwater harvesting system?

For a domestic system to flush toilets and feed the washing machine, you will require a second dedicated plumbing circuit. This prevents the possibility of cross-contamination between rainwater and your drinking water supply.

Since the rainwater being supplied to the house is normally pumped to the building via a pump in the rainwater harvesting tank, you must use green and black supply pipe to identify it as reclaimed rainwater. This is to avoid any possibility of someone confusing it with drinking water in the future.

All internal plumbing has to be labelled to identify it as rainwater. The stopcock and outside taps should also be labelled to ensure there is no confusion by users as to the nature of the water.

During a new build or renovation, the extra plumbing is relatively easy and not very costly. However, to install this plumbing in an existing building would be extremely difficult making a domestic rainwater harvesting system not suitable for existing houses.

How much filtration does rainwater need to reuse in toilets?

Rainwater is perfectly clean enough to use for toilet flushing. Keeping it that way is another matter. The introduction of leaves that have fallen on the roof is the main factor in how clean the water will be. When leaves get wet they break down into a mud-like substance which will dirty the water. We, therefore, add a leaf filter to the tank to ensure that the leaves are kept out. It is good practice to check the leaf filter around the time that leaves are falling; it’s a five-minute job and will keep water quality at its optimal level.

Our domestic systems also include:

  • A calming inlet to prevent any disturbance in the water in the tank
  • A fine filter before the pump
  • A fine particle filter after the pump

If the system has had its leaf filter checked and cleaned regularly, then the fine filters should only need to be checked every 3-5 years. This will depend on how clean the water is in the main rainwater tank.

Where can I locate a rainwater harvesting tank?

You can locate an underground rainwater harvesting tank in the front or back garden, with some tanks, under a patio or under the driveway are also possible. Location of an above ground tank is a little more flexible; however large tanks can be unsightly and can require hiding, depending on the aesthetics of the property.

You must ensure you are not impacting the foundations of a building when installing an underground rainwater harvesting system. A rule of thumb is to install the tank twice as far away from the building as the depth of the hole. Therefore, if the hole you are digging to install the tank is 1.5m deep; install the tank 3 metres away from the building. Consultation with your local building control is advised.

How far away from a house can a rainwater harvesting system be?

The pump in a rainwater harvesting system can normally pump the water very far. We would however suggest that if you are installing the tank more than 25 metres away from the building, you should use a larger bore pipe than the standard 25mm pipe (32mm pipe will be fine).

If you do plan on installing the tank very far from the property, please consider that your drainage pipes must be at a gradient to allow water to flow. If you have a long drainage run into the tank, it can put the tank deep in the ground, which is not advised. If this is the case, consider installing the tank closer to the building to keep the tank shallow.

What’s next?