Rain Water System and Grey Water System at 281 Redcatch Road.

(Also with a note on Solar Panels.)

General plans and implications for Architects and Builders while the building is being extended.

The proposed Rain Water System (RWS)

The aim is to not let any rainwater from roofs or from the ground surface (e.g. car port or drive and the patio) to enter the town drains, not even rain from a cloudburst or exceptional rainfall over a period of time. The Water Co give a small reward for this, but the motivation is 'Green'.

All rain onto our roofs is to be routed to a collection point near the south corner of the new extension (i.e. near the shed, which I shall call the “South Shed”).

The collected rainwater will be stored in one or more large butts near the South Shed.

Rainwater downpipes from roof gutters are to go to water tubs or butts, (c 100 to 200 litre) one in front, one at back of house. Will need mains connection. Will need pipe to outlet near South Shed.

The stored rainwater will be used mainly for:
a. augmenting the Grey Water System, i.e. to be used in the WCs in the house
b. replenishing the ornamental pond.
c. watering the garden.

OVERFLOW and surface run-off.
The original plan was (and I hope may continue to be) that overflow from the collection system (and surface run-off) is routed onto the lawns. Both the lawns, the one at the front of the house and that at the back, have been landscaped such that excess water would be trapped on the lawn to a depth of about 10cm. The front lawn is approx xxx square metres, The back lawn is approx yyyy square metres. Thus each will hold up to zzz cu metres. The roof area will be approx Sq Metres so each mm of rain will produce cu metres of water. The average rainfall in xxx the month with the heaviest rainfall on average is mm.

The plan was to observe the effects of unusually high rainfall and if necessary construct one or more standard 1 cu metre soakaways to augment the soakaway effect of the front and back lawns and flower beds.

However a recent pamphlet from the Water Company suggests that all rain must be routed to standard soakaways, not to rain water butts. If this is the case this rule is hard to understand. A later version of this document will clarify the situation.

The car parking space at the front of the house is currently mostly permeable and it will eventually (on completion of the building works) be entirely paved with permeable materials. At present the concrete part of it drains into the permeable part. In the future any run-off will be routed to the front lawn. There will be a grating-covered gully along the boundary of the property and the highway, with water routed onto the front garden.

The patio at the back of the house also consists of permeable brick and slopes such as to route run-off onto flower beds. Any extension of this patio will keep to this scheme.
In the two years since this patio was installed we have never observed surface water more than approx 2 mm deep and it has never been seen to persist form more than half an hour.

Grey Water System (GWS)
The purpose of the GWS is to re-use some household waste water that would normally go into the town drains. The water will be processed then stored for use to flush the WCs and will also be available for watering the garden.

Collection. In the kitchen a second sink normally used for rinsing will have its drain routed to the GWS.
Baths, showers and wash basin will also be routed to the GWS.
House rules will attempt to ensure that very dirty water, or excessively soap-laden water, will not be put into these drains.
Bathroom users will be asked to pour particularly dirty or soapy water into the W.C.

Technology for collection..

The drain from each appliance (wash basin, shower etc) will go to a lidded trap either (preferably) just above floor level in the Utility room, or just below ground level either in the floor of the utility room or outside. Capacity 5 to 10 litres.
In the trap there will be a submersible automatic pump, or submersible pump and a water level sensor. Probably mains powered, so a suitable wall connection will be required. The pump capacity should in the range 10 to 20 litres per minute. If and when the pump cannot pump all the water coming in, the water overflows to the town drain. The pump output will be routed to the grey water system processing near the South Shed.

Use of Grey water.
The normal WC supply cisterns will be fed from an additional cistern (the "GW cistern") located in the roof space.
The GW cistern will normally be fed with water from the GWS storage tank by a pump near the storage tank, which will be actuated by a sensor near the top of the GW cistern.

In case the GWS fails to provide sufficient water the GW cistern will also have a supply of mains water via a ball-cock located near the bottom of the GW cistern. Initially this will be the only source of water for the WC cisterns.

Overflow from the GW cistern will be to the exterior, in such a place as to attract attention. (e.g. onto the front door porch!)

I am hoping that Paul can construct the trap and the GW cistern, including provision of the sensors and suitable ball-cock. (I am assuming these devices are not readily or cheaply available. ??)

It would be good if a suitably qualified person could check my estimates of capacity of stores and pumps.


I hope the necessary infrastructure can be incorporated into the work on the extension.

It would be helpful if Henry could estimate the additional cost of the RWS and GWS in case we decide to fund these installations from a different financial source.

As far as the current building work is concerned I would hope:

1. That for the RWS, we install and re-install the roof gutters so as to bring all the rainwater to two downpipes, one at the front, one at the back of the house with pipework installed from these butts to near the South Shed. Electric power outlets will need to be provided near the butts, to power the submersible pumps which will be installed in each butt.

2. That we install pipework from all washbasins, baths, and showers and the rinsing sink in the kitchen to the sump in the Utilitiy Room (or to one outside)

3 . That we install pipes :
a. to carry the collected waste water from the sump to a point in front of the South Shed
b. to carry cleaned grey water from near the shed to the GWS cistern in the roof space.
(The GWS processing/cleaning equipment will later be installed near and behind the shed.)

4. That we install the GW cistern with its mains water supply in the roof space. (The GWS cistern will be supplied by me, probably constructed by Paul). And the pipework to feed the WC cisterns from the GW cistern.

The connections beween the house and the RWS/GWS equipment near the south Shed could be via a channel with a removable cover across the side access path at the side of the house, for these pipes and for power and control wiring. Alternitavely they could be underground, in which case more cables and pipes than specified here should be included so as to allow for future developments.

Summary of pipes etc. across footpath, i.e. to and from house and South Shed area):

Rainwater collection pipes (2)
Grey water collection pipe
Grey water supply to roof space
Wires to Sensor in GW cistern
Power for the the GWS pump (and for the South Shed)

Extensive use of in-pipe stop cocks to facilitate later modifications.


1. Water heating
The currently installed hot water solar panels will need to be moved to the new roof.

1. a. . I am working on a plan to add a heat dump, in order to stop the water reaching boiling point, which has several disadvantages. This would involve additional pipework and control.

2. Electricity Generation.
I intend at a later date to install PV panels to generate electricity. Currently I have no detailed plans. But we need to aim to maximise the amount of roof area facing in a southerly direction.


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