Rainwater butt buying guide
Jeremy, construction site supervisor, Cardiff128 guides
- Water consumption
- Exterior tank
- Underground tank
What would I need a rainwater butt for?
For ease of use, we drink more and more tapwater. The average consumption per person is estimated at 200 litres per day! Approximately 50% of this water is not linked to human thirst (toilets, wahsing machine, cleaning etc)
Watering a garden or irrigation of a vegetable garden also consume a lot of water, without mentioning swimming pools and washing cars.
So many litres of water are lost, which you pay for, and often at great expense
Other than economic factors, you should also consider that water is not for granted. The avergage level of phreatic tables are steadily decreasing over the last 30 or so years. The distrubtion of high quality drinking water has become a real challnge for public services and these companies are often corporate for both the networks and treatment. These are juts as much reasons to reduce your water consumption by installing a water butt!
Ok, but how does it harvest rainwater?
It couldn't be more simple! The rain that falls onto your roof is channelled by the gutters towards the tank to be stocked. In general, whatever the purpose of your installation, a basic filter is installed before the entry point of the tank (mainly to keep leaves out).
If you have opted for an exterior tank, the distribution of the water is carried out by gravity thanks to a simple tap at the bottom of the tank, or with a pump.
If you have opted for an underground tank, the distribution can only be carried out using a pump. At the exit point, a valve (also called an overflow) is directly hooked up to the waste water system for rainwater to avoid any floods!
What type of butt do I need?
It is of course the first question you need to ask yourself! The type of but is driectly linked to your needs and as we have already seen, there are two different types.
- Exterior tank: it is very rare that this type of water is used for sanitary purposes. Given the low volume of the tank, the water but is mainly used for watering, irrigation, or to wash your tools or your car for example. It can be easily installed and does not require any difficult work on your existing waste water disposal sytem. Thanks to a collection point which is fixed to the drainpipe leading from your gutter, the rain that falls onto your roof is directed into the tank. The overflow of the waterbutt is hooked up direcly to the same waste as your original drainpipe. The capacity of exterior tanks varies from 200 to 2000 l and they are largely made of polyethylene as they are light to work with (empty!). A basic filter should be installed before water enters the tank. More often than not, this is a simple grate at the top of the draipipe. This avoids leaves from going into the tank. As for distribution, You can simply let gravity do its job by putting a tap at the bottom of the tank. The majority of tanks are equipped with a 2" threaded outlet allowing you to add a stopper or a valve. You can also opt for an immersed pump which can be placed at the bottom of the tank. This pump has a float based level sensor which has the rold of stopping the pump when the lower level of water has been reached. You can also attach a hosepipe or a pressure washer. The power and the debit of the pump can be chosen according to the volume of your tank (as a reminder, 6 m3/h = 100 l/mn).
- Underground tank: installing this type of tank allows you to use not only rainwater for outside purposes (watering, cleaning etc.) but also for sanitary purposes (toilets, washing maching, non-drinkable water tap). Indeed, their large capacity brings you the confort of use with a certain automnomy. Their volume varies between 1500 and over 5000 l. These tanks can be made of polyethylene or of concrete. Their installation requires precaution of several constraints. You must dig a hole in the ground to install the tank near a drainpipe and near to the point where you can connext the canalisation for distribution within your home. The installation in itself is also a little complex as, as well as the basic filter at the top fo the drainpipe, you must install a filter before the tank's entrance to limit fine dirt and impurities whihc may come from your roof. An overflow must also be attached to your rainwater waste evacualtion. For the distribution, a pump must be installed and may have several functions.
- manual start/stop by an immersed pump at the bottom of the tank for outside use only (for wateing, cleaing etc.) ;
- high-pressure where an pump outside the tank automatically starts when water is drawn (depression). This type of pump is placed outside (watering, cleaning...) or inside the home when you pull the flush, the washing machine starts, etc...).
What volume should I choose?
For your basic outdoor usage, a minimum volume of 1500 L is recommended. If your property is relatively big (> 100 m²), you can calculate your needs based on 15 L/m².
For sanitary usage, you usually need 5000 L for a 5-person household. You can add 1000 L for every person.
For a mixed usage (outdoor + sanitary), simply add those volumes up.
Example: for a 5-person household with a property of 150 m², the minimum recommended volume is of: 5000 + (15 x 150) = 7250 L, hence a 7500L sized water butt (closest greater size).
You also need to set-up a specific distribution network around your home, for the water collected.
Are there any regulations on water butts?
As with anything, you will need to install the rainwater harvest system in accordance with the manufacturer's instructions. All installations should be in compliance with national building regulations and Water Supply (Water Fittings) Regulations 1999. You can get more information on these from local suppliers, the Water Regulations Advisory Scheme21 (WRAS) or the UK Rainwater Harvesting Association (UKRHA22)
Always remember, if you are planning any alterations to your home drainage network they will have to be applied to Building Regulation and you may need to apply for Planning Permission. The Building Regulations which specifically relate to water and drainage are Part G: Sanitation, hot water safety and water efficiency, and Part H: Drainage and waste disposal.
As with all questions of waterworks, you will need to make sure your installation is WRAS compliant. Accordinf to the Information and Guidance Note 9-02-05:
- pressure and electricity standards must be checked
- all pipework must be labelled (so that you dont mix drinking water with rainwater)
Can you give me an idea on water consumption?
The best way to calculate your water consumption is with the following:
- watering the garden: 15 L/m²;
- washing a car: 200 L approximately
- using a pressure washer: 300 L per hour
Any last advice?
To benefit from your water butt on the long term, it is recommended, whatever the installation, to drain and fully clean the tank at least once a year.
If your usage of the water butt is mainly sanitary related, you should regularly clean all filters of your installation to avoid clogs, obstructions, and any other type of pumping issue.
If you’ve set-up a pump, whether underwater or not, it is highly recommended to regularly clean the suction strainers (at least once or twice a year).
And don’t forget to check your gutters every now and then, in order to clean them from any leaves or moss coming from your roof.
For our friends living in the colder regions of the UK, please don’t forget to drain and empty your tanks before the winter, to prevent the frost from damaging your water butt!
Jeremy, construction site supervisor, Cardiff 128 guides écrits
for 4 years now, I am restaoring and bulding an extrension to a bungalow in the heart of the welsh countyside. My experience in manual work and my knowledge means I am proud to be of service. Terraces, interior design, roofing, plumbing, electricty, anything goes! We have, my wife, daughter and I, built almost everything we have from scratch! So to answer all of your questions, and to orientate and advise you on coosing your tools? Easy!
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