FREQUENTLY ASKED QUESTIONS  

About Rain Water Harvesting

What is rainwater harvesting?
It is the collection from roofs of rainwater that would otherwise flow down gutters into drains or a septic tank. This water is stored in tanks ranging from 200 litres upwards. 
Larger ones can be installed underground. Filters and pumps can also to added to keep collected water cleaner and make distribution easier. The larger the tank you have, the more money you will eventually save and the more protection you will give your garden during droughts and possible hosepipe bans.

What can you use rainwater for?
Rainwater can be used for all outdoor uses: watering the garden, washing cars, cleaning patios, drives and windows, topping up swimming pools, ornamental ponds and hot tubs. With some plumbing alterations, it can also be used inside the house to flush WCs and feed clothes washing machines. Besides saving on drinking water use, rainwater use encourages less build-up of calcium deposits in appliances.

Why should I use rainwater?
Each person in the UK uses about 160 litres of drinking quality water a day. Nearly half of this amount need not be drinking water. It seems crazy to bring in drinking 
water from miles away via your water board to water your garden or clean your car when you could provide water directly from your own roof. It is now recognised that the south east of England in particular is short of water (London has less water available per capita than Madrid or Istanbul). April 2007 was the driest on record, but then June 2007 was the wettest on record. That's when the wags started asking when the hosepipe ban would start! The more water you can collect in wet spells, the more you will have when it's dry.

Is rainwater better than drinking water for outdoor use?
Your garden will prefer rainwater to tap water because it does not contain the chemicals needed to make tap water drinking quality. And when using a cleaning agent, you will need to use much less, again because there are no chemicals and the water is softer.

How will rainwater harvesting help me during a hosepipe ban?
Last summer many areas had hosepipe bans banning watering gardens and cleaning cars. New proposals will give water boards the right to prohibit using hosepipes for other outdoor cleaning purposes such as washing boats, patios, drives and windows, and also for filling swimming pools, ornamental ponds and hot tubs.

Will I save on my water bill if I have rainwater harvesting?
This depends on your water board and your circumstances. You are more likely to save on your water bill if you have a meter. Government reports estimate that 70% of customers see their bills reduced with a meter. Meters reduce water consumption in households by 10 to 15%. Most water boards have ready-reckoners on their websites to help you decide whether a meter is a good idea. Currently only around 23% of households in the UK have meters, but as metering appears to have such a beneficial effect on both the consumer and in reducing water consumption, the government is considering making water boards in southern England make meters obligatory.

If my water is not metered already, can I ask to have one installed?
Yes, all water boards have to install a meter at the request of the householder. Installation is free, and some boards provide the meter as well. Some water boards insist on installing a meter with change of ownership, and sometimes, in tenancy of a property.

Planning my rain water harvesting system for garden use

What size tank do I need?
This depends on a whole range of factors: where you live (amount of rainfall a year), the roof area available, what you want to do with the water, the size of your garden, how much drought protection you want, whether you want to use the rainwater inside the house for WCs and the washing machine. The tank size calculator on this website will help you work out your needs.

Does the tank have to be underground?
You should weigh up the arguments for and against digging your tank into the 
ground…
1) in favour of digging the tank in:
    a) No unsightly equipment in the garden, especially if you are installing a tank 
bigger than 200 or 360 litres
    b) Suitable for a small garden or where the space is otherwise restricted. For 
example, our stronger tanks can be installed under a drive way if suitable 
supports are constructed over the tank
    c) Less risk of brackishness in summer due to warming of the leaf debris at the 
bottom of the tank. However, a properly filtered system will not be subject to 
leaf debris and brackishness in any summer conditions
    d) Negligible risk of frost damage to tank, piping and pumps in winter. Take into 
account the prevailing temperature conditions in winter where you live; if your 
pond or water trough freezes up seldom, and if the layer of ice is only a few 
centimetres thick at worst, then your rain water harvesting tank and 
equipment are unlikely to be damaged.
2) in favour of situating the tank above ground:
    e) Much cheaper and easier installation costs
    f) Easier to maintain in case of change of scenario or pump failure
    g) Suitable for farm, outhouse, stable and other installations where the visual 
and aesthetic criteria are less important

Do I need a large roof area to provide an adequate supply of water?
A surprisingly small roof area will give a lot of rainwater: a typical terraced house with a 6 by 8 metres roof area could give 30 000 litres a year depending on the area of the country you live in. Check the tank size calculator and UK rainfall figures on the www.RainWaterHarvesting.co.uk web site.

How long would the water last in a drought?
Check the tank size calculator on the www.RainWaterHarvesting.co.uk web site. You can calculate from the size of your roof and average rainfall figures in your area (available on our web site) how much water will come off you roof in a year. The same calculator works out how long the water will last in a drought from a) your garden size, b) how much water you want to give to your plants, and c) the size of your tank.

What else do I need besides a tank? 
A filter installed in the down-pipe to the tank is a good addition for all tanks but is 
particularly to be recommended for larger tanks installed above ground where water may be stored for a longer time. It will help prevent water becoming smelly by removing leaves and other debris. This also stops sludge accumulating at the 
bottom of the tanks, and tap outlets, hoses and water-can heads clogging up. Some filters separate debris out and send it on down the drainpipe. Other filters eject debris straight out the side, while cleaned water goes into the tank. Both kinds are easy to maintain. 
For even cleaner water, an overflow siphon collects smaller particles such as pollen 
which can accumulate after filtering on the top layer of rainwater. It also stops vermin falling into tank through the overflow outlet.
A pump makes distribution from the tank easier by maintaining a good pressure. 
Pumps (such as our Forta Duo pump) with a pressure switch-off allow you, for 
example, flexible watering. When using a spray-head, you do not have to run in to 
turn pump off: it will stop when you click the spray-head to off. Other less expensive pumps will only stop when the water level in the tank is too low for it to work any longer. Another useful accessory is the floating pump intake in the tank which ensures that only the cleanest water from the top enters the pump. Although pumps do have their own filters, they perform much better if the rainwater has been filtered already by an exterior filter.

Why is it a good idea to install a filter and pump if I am only using rainwater for 
the garden?
A filter installed in the down-pipe to the tank is a good addition for all tanks but is 
particularly to be recommended for larger tanks installed above ground where water may be stored for a longer time. It will help prevent water becoming smelly by removing leaves and other debris. This also stops sludge accumulating at the 
bottom of the tanks, and tap outlets, hoses and water-can heads clogging up. Some filters separate debris out and send it on down the drainpipe. Other filters eject debris straight out the side, while cleaned water goes into the tank. Both kinds are easy to maintain. 
A pump makes distribution from the tank easier by maintaining a good pressure. 
Quality pumps (such as our Forta Duo pump) with a pressure-sensitive switch turn 
themselves off when water flow is not needed; when using a spray-head, you do not have to run in to turn pump off: it will stop when you click the spray-head to off. Other less expensive pumps will only stop when the water level in the tank is too low for it to work any longer.

What is the best kind of pump to use?
Pumps (such as our Forta Duo pump) with an automatic pressure switch off and 
which can be used both in and out of the tank are the best. These allow you, for 
example, flexible watering. When using a spray-head, you do not have to run in to 
turn pump off: it will stop when you click the spray-head to off. Other less expensive pumps will only stop when the water level in the tank is too low for it to work any longer.

What size pipe should I use?
a) Butts and tanks 1000 litres or less, do-it-yourself systems:
It is tempting to use a small diameter pipe (hosepipe or 25mm (one inch diameter) from the collector-filter to the tank. However it is worth the effort to use 32mm pipe. A narrow pipe will collect the bulk of water from light rain and drizzle, but during the critical period of collection, i.e. the summer, you need to be ablt to catch the available water which typically falls in sudden storms at that time of year. So give yourself a chance by fitting the biggest pipe possible. In our experience, 32mm is the best. Try to buy usually Spiroflex or a similar pipe which keeps its shape (transparent tubing from a DIY shop twists and caves in, restricting water flow, so avoid it). You can get Spiroflex from any aquatic or fish pond supplier, often in the back of your garden centre, or order it from us. The connection kit with the £P filters is available seperately on request. b) Tanks larger than 1000 litres and all underground tanks, professional systems :
Rigid piping is recommended, 75mm or 100mm in diameter so that the flow is unrestricted and so that the weight of earth or backfill does not collapse the pipe. installations of this sort would normally be installed by your contractor or plumber.
When do I need to use a filter?
A filter is recommended in every Rain Water Harvesting installation. However it is 
most critical when leaves often fall on the roof being used, such as a low roof with 
trees nearby.

What is the best filter to use?
Rain Water Harvesting sells two types of filter. 1) The down-pipe filter takes the water feed for your tank through an outlet in the side; the leaves or other debris continue down the existing down-pipe from your gutter. Use this next to the house when adapting an existing down-pipe. When the tank is full, excess water flows on down the down-pipe. 2) The leaf extractor pushes leaves or other debris out of the side of the filter and it's the clean water that continue down the down-pipe. Use this type on out-houses, garden garages, stables etc when the down-pipe goes straight into your harvesting tank and when you don't mind leaves being pushed out the side. 

Is there a risk that the down-pipe filter causes a back-up spill over the gutter?
Both down–pipe filters and leaf extractors have overflow capacities as big as the 
original down-pipe to which they were fitted. You might get back up of water and 
overflow at the level of the gutter, but only in such extreme rain fall that you would 
probably have had gutter overflow anyway.

Of the three filters currently on our web site, the affordable Rain Filter Collector 3P-2000820 is a must for rain harvesters. It features an automatic overflow and removable filter and has a facility for connecting a 32mm diameter output pipe to the rainwater tank. If there is a storm then this pipe would collect more of the water than a 25mm pipe of course.

Of the other two, VF1 is optimised for underground tanks, and Rainus, which expels 
the leaves to the side, would be ideal in a semi-agricultural case where you would not mind the leaves coming out the side.

Why do I need a siphon?
The siphon skims small particles of dirt off the top of the water by creating a more 
rapid water flow from time to time. This is rather like the flush of a toilet but on a 
smaller scale. It keeps the water in the tank cleaner than a plain overflow pipe.

Can I use a small butt near the house feeding a larger tank elsewhere?
Yes. You can have a small water butt (say 200 litres) collecting rainwater off the 
house down-pipe. As it fills, an automatic level-sensitive pump sends the water 
through an above-ground or buried hose-pipe or 1 inch pipe to a much bigger storage tank underground or elsewhere on your property. You should plan for a soak away to handle excess water at the storage tank.

What is the best watering system to use with a rain water harvesting tank?
Choose the system which is best for you. 1) Fill a watering can from the tank, 2) 
Hose or tricklers fed by gravity from the tank. 3) A level-sensitive pump which stops when the level in the tank drops to a pre-determined level. 4) A pressure sensitive pump which turns off when it senses back pressure in the pipe it's feeding, e.g. when you close the sprinkler or tap with which you are doing the watering

Am I obliged to put my water butt on a pedestal to get the watering can under the tap?
No, if you are going to use a pump. And even without, attach a short length of pipe to the tap and water will flow into a watering can or bucket until the level of the water in the butt is lower than the level you want in the can.

Does all rainwater harvesting equipment come with all the right connectors?
In a word, no. We have been surprised at how lacking in diligence most of the manufacturers have been in this respect. Here at Rainwater Harvesting we make every effort to inform buyers what they're getting and we'll source and provide any extra bits needed. Look out for the RECOMMENDED sign against kits in our web shop. If you buy hose, try to use 32mm spiral reinforced all the time. Flow is better and connectors easy to get.

Can I use rainwater in my pressure cleaner?
Yes but with a suitable pump. Most pressure cleaners, like the Karcher, needa certain amount of pressure and flow rate of the water at arrival. We have found that the small pumps in the £30-£50 range do not deliver enough pressure, but better ones like the Forta Duo 3P-6000450 work fine.

Can I use rainwater to fill a swimming pool?
Yes. Use Rain Water Harvesting tanks, pumps and filters to ensure that the water 
being fed to a swimming pool is well filtered. Check your alkali level and other water factors after filling with rain water.

Domestic systems

Can I use rainwater in the house?
RainWaterHarvesting.co.uk does not supply all equipment for domestic piping, but our tanks, filters and pumps are often used in such systems. Use rainwater to flush the toilets and wash the clothes, as well as the garden.
Use of rainwater in the house requires you to plumb a second network of pipes in the house to feed rainwater to the appropriate places. You should keep the rest of the mains network seperate so that mains drinking water is piped to the kitchen. The use of rainwater for baths and showers is a) a question of your own and authorities' assesment of the risk of contamination of the rainwater supply by dirt, brackishness or bacteria, and b) requires you to install a secondary hot water system for rainwater as well as the secondary hot water system for rainwater as well as the secondary cold water system for rainwater. These factors influence many users to use rainwater for toilets and clothes washing only.

The "Rain Manager" RT-N-SRB unit (picture right) at about £770 from RainWaterHarvesting.co.uk enablesyou to connect the rainwater tank to your mains water system in such a way that the mains water is switched back on when the water tank dries up. A cheaper alternative is to rig a tap to turn off the supply from the rainwater tank and a tap to turn on the main water supply to the secondary rainwater piping - but this requires rigorous manipulation so prevent the mains water flowing back into the rainwater tank and out of the overflow.

Some suppliers recommend systems where the mains water is used permanently to top up the rainwater tank. This works fine except that the rainwater tank is then always full and you lose the benefit of any new rain shower.

Do please check with local authorities about any regulations that might apply.

If I use rainwater in the house, what happens when my tank runs out?
Professionally-installed rain water system in the house include an electronic switch 
which switches back the mains water supply when the level of rain water drops below a useable level, or tops up the rainwater tank. These systems can work whether you have a pressure mains water system or a header tank in the roof space.

What is grey water?
Grey water is waste water from the house (from basins, showers, baths, washing 
machine and dish washer) but not toilet wastes and food wastes derived from 
garbage grinders (called "black water"). It's mostly a question of personal taste 
whether to use grey water to water the garden, but if you are not a heavy detergent user, then, yes. Grey water should not be used to fill swimming pools and it might give a smeared finish when washing cars You should consider a specialist treatment plant (http://www.greywater.com) and you should also check any applicable regulations.

Is it better or easier to use rainwater than grey water?
Rainwater is better than grey water as rainwater contains less detergents, soaps, 
chemicals and bodily dirt. But in times of severe water shortage you should try to 
store grey water for garden use.

What are the installation requirements for a large underground tank?
a) If the ground where the tank is to be installed is well drained and has a low water table, back filling with sharp sand, earth or pebbles is OK. You are advised by 3P to provide a concrete base of 150mm under the tank.
b) If the ground is habitually wet or the water table is high or the tank is to carry a load, the tank should be concreted. PE tanks are not normally strong enough to keep their shape in compression so the tank must be filled with water as you proceed with the concreting.
Please consult in detail the installation guide which you can get by emailing us.