1. Grey Water In UK Buildings By Tom Bishop
grey water and its reuse with in UK buildings
By Tom Bishop

2. Contents What grey water is Why recycle it How its treated
Applications
Potential savings
Future prospects
I will start by explaining what grey water actually is and why we should bother to recycle it
Move on to treatment methods and applications of grey water within a home.
Finally I'll look at potential monetary and environmental savings

3. Typical Domestic Water Cycle
Black water plumbing
White water in
Domestic use
Grey water plumbing
Sewage network
Water treatment facility
So here is a basic outline of domestic water within a house hold;
Treated potable water also known as white water arrives from treatment facilities where it has been highly treated so that it is potable, i.e. fine to drink.
Treatment facilities purify contaminated water through a combination of: chlorination, aeration, coagulation, sedimentation, filtration, desalination and disinfection
All to get the water so it is fit for human consumption..
to be fit for human consumption there are thousands of physical, chemical and biological parameters that must be met.
Treated water is then used for a huge range of purposes, drinking, cooking, washing, flushing toilets, cleaning cars etc. etc., many activities which do not require such a high quality of water.
Next the waste water is transported to the sewage network, typically with in building grey and black water are kept separate until leaving a building, making reuse of grey water on the surface relatively simple

4. Grey and Black Water Grey water: Typically no pathogens
Reduced bacteria
High biological oxygen demand
Black water:
Pathogens
Bacteria
High biological oxygen demand
Grey water is distinguished from black water in that it originates from sources far less likely to carry disease causing pathogens
Grey water makes up around 60% of waste water with in a domestic household
Typical sources are found in the kitchen, laundry rooms, bathrooms, sinks etc.,
basically sources which water is unlikely to contain disease organisms of anywhere the same magnitude as those in toilet wastes. By far the greatest source of pathogens in wastewater is faeces (poo).
Black water accounts for around 40% does not decompose effectively enough for reuse in any application without a risk of contamination. In comparison, grey water generally requires minimal treatment for reuse, dependent on the application and pollutant levels involved, il go in to some examples of this later.
Although grey water is far less polluted and dangerous than black water it is by no means as safe as treated mains water (known as white water). if untreated for several days grey water will become malodorous and anaerobic due to increased Biological oxygen demand (BOD) from the action of increasing numbers of bacteria.
Contrary to black water, grey water is not malodorous immediately after discharge. However, if it is collected in a tank, it will very quickly use up its oxygen and become anaerobic, which known as the septic grey water.
Once it reaches this septic state, Septic grey water can be as foul-smelling as black waste and will also contain anaerobic bacteria, some of which can be human pathogens. Consequently, a key to successful grey water treatment lies in its immediate processing before it turns anaerobic

5. Why bother to Recycle Grey Water?
Growing Water demand:
Changing climate
Increasingly water intensive lifestyle
Urbanization
Population growth
Increasing usage in industry and agriculture
Areas of relative water stress
A fundamental question asked by people new to grey water is why bother to recycle it when the UK if far from arid and having a plentiful and relatively consistent supply from the heavens in comparison to much of the world,
The UK is not seen as having issues when it comes to water supply, however there is a growing demand on the mains water supply
In fact The South East and East of England have been classed as having serious water stress. The drought of was only managed through controls on what we could use water for (like the hose pipe and sprinkler bans). This was not a one-off; indeed droughts are likely to be more common. By 2080, some long term climate
projections for the south east forecast 50% reduction in rainfall in summer with only a 30% increase in winter, meaning a reduction in annual net rainfall as well as longer dry periods.
Admittedly water supply issues associated with the UK are very unlikely to ever reach a level where they are causing disease and fatalities. However this does not mean the current situation should be ignored and improvements not made where possible.

6. Why bother to Recycle Grey Water?
Is rain water free?
Costs in..
Collection
Treatment
Transportation
Leakages
Because the UK currently has a good supply of water through rain does not mean this water is free of cost:
Associated costs with such ‘free’ water are considerable for it to be fit for human consumption, which the vast majority of household tap water is; including the hot water tap (although some people get a bit funny about it as it has been sat in a boiler for a while.
Anyway, this supposedly free water needs be collected, undergo intensive treated and then be pumped from reservoirs, rivers and aquifer where it has been stored large, over distances to household taps for usage. And due to leakages in water network infrastructure for every one litre of tap water we use approximately 1.5 litres of water had undergone treatment
All of which has a large cost in terms of both money and to the environment.
One litre of reused grey water effectively saves treatment of around 1.5 litres of water.

7. Why bother to Recycle Grey Water?
More efficient water usage
Only 7% of household water is used for drinking and cooking
Large levels of potable water used for activities which do not require high quality water e.g.:
washing cars
flushing toilets
Irrigating gardens ?
In terms of efficient usage we currently use potable mains water for a vast Range of applications; for brushing our teeth, filling a glass to drink,
taking a shower in the morning or preparing food. But we also use this water to heat our homes and offices, clean our clothes, water our gardens, wash our
cars and in many other activities which do not require such a high quality of water.
Around 7% of the water used in our homes is used for drinking and cooking. Almost one third
of the water we use is, after being treated to what is among the best drinking water quality standards
in the world, at significant financial and environmental cost, simply used to flush our toilets
infect it has been estimated only 6% of mains water supply is used for activity's which require such a high quality of water

8. Treatment Primary treatment – Settlement tank Costs
screens out scum (oils & greases) and sludge (course solid particles)
Costs
£200 to £ for tank depending on size
There are four reasons why grey water may need to be treated:
1. To remove substances that may be harmful to human health.
2. To remove substances that may be harmful to plants and soil.
3. To remove substances that may be harmful to the environment.
4. To remove substances that may clog the irrigation system.
In general, primary treatment is considered the most economically attractive system as it requires relatively little maintenance and does not depend heavily on electricity or chemicals. Once passed through the septic tank the grey water is suitable for subsurface irrigation many plants.
 BOD removal efficiency 48%
COD 20%

9. Treatment Secondary treatment – Sand filter Total system costs
£500 to £2000 for basic filter systems
£2000 to £ for fully integrated building system; including pumps pipes tanks etc.
Grey water from settlement tank
Fine sand
intermittent or slow sand filter
reducing bacteria by between 90 and 99%.
BOD removal efficiency90%
COD 80%
Gravel
Filtered water out

10. Treatment Secondary treatment - Wetlands Costs
From settlement tank
To irrigation
 COD removal efficiency70–90%
Costs
Approximately £100/m2 (surface area)
2-3m2 required for 100 litres per day throughput

11. Applications Toilet flushing
Sloan AQUS Grey water System- Small scale stand alone, £400
Filter with chlorine tablets
30% reduction ??
Customers claim approximately 8 year payback time
Probably the most common and widely mentioned application of treated grey water is in using it to flush toilets, Often water only needs to be coarsely filtered and have a simple disinfectant applied to it, like chlorine.
Toilet flushing accounts for around 30% of a house holds potable water usage, a typical single flush of a toilet uses between 9-12 litres of water, even ‘water efficient’ toilets still use between 4 and 6 litres per flush. Across the UK it is estimated around 2 billion litres of white water are flushed away every day.
So it would seem there is a great potential monetary savings for individual household and environmental benefits.
There are many different systems available with ranging costs and efficiencies:
A low cost solution to reuse of grey water is the Sloan AQUS Grey water System costing around £500 per toilet and is self fitted, its basically a box which collects bath room sink water, filters it, adds chlorine and then pumps it to fill the toilets cistern. the company claims reduction in water usage of up to 30%, this however I think is very optimistic claim as this is basically saying the system will supply all the water for toilet flushing. This is unlikely as a typical sink usage will not be enough to fill a cistern so the cistern will have to be topped up with mains water to be able to flush efficiently. This in itself leads to issues with grey water being back siphoned into a buildings white water supply, which can be overcome but adds complication and hassle to the insulation and probably above the skill level of your average Joe to complete
subsurface drip ($1500
Another way of indirectly reusing grey water is through heat exchangers..
DEFRA hot water use in our homes – for things like
washing, bathing and cooking – is responsible for 35 million tonnes of greenhouse gas emissions each
year: over 5% of total UK greenhouse gas emissions. Water efficiency measures, particularly those
that focus on hot water use, are therefore doubly beneficial, with water as well as greenhouse gas
savings. We must do more to promote these types of water savings which have multiple benefits

12. Applications Toilet flushing
Aquawiser residential Grey water System- fully integrated
£2000-£3000 for typical 5 person house
Actually achieves 30% reduction
Mains top up
Overflow
To cisterns
Treated grey water
Grey water from bath/shower to treatment
Or there is fully integrated systems like the Aquawiser residential grey water system:
Grey water from baths and showers is diverted to and underground tank where it is treated to a higher standard compared to the sloan Aqus, so it can be stored for longer. Its them pumped up to a short term storage tank at the top of a house, then under gravity it fills all the toilet cisterns with in a house.
With the water consumption being slightly higher for bathing compared to toilet flushing, there is enough grey water to flush the toilets and often enough to also back wash the filters within the Aquawiser. If however your house hold washes less than average and flushes more than average then the water supply can be topped up with mains water, there is also an overflow pipe for if there is too much grey water to stop mains supply being contaminated.
Again this company claims up to 30% reduction in water bills which I see as much more realistic than the previous example.
They do not give any figures for payback time however its likely that larger buildings will have a reduced payback time as the system will be more efficient in larger buildings as the initial financial outlay will not be much more than smaller buildings, where as the throughput will be greater and hence increased savings.
I will make estimates of these savings and payback later.
Treatment tank & pump

13. Applications Irrigation
Primary treated grey water - Subsurface irrigation
Secondary treated grey water – surface micro drip irrigation.
Another application of treated grey water is for garden irrigation. Upper soil levels are quite biologically active and actually help to further purify the grey water. Also grey water often contains nutrients such as nitrates and phosphates found in detergents which are beneficial to plant growth, how ever harmful chemicals are also found in many grey water sources such as sodium and chlorides, so the source of grey water must be considered in irrigation.
Once grey water has passed through the settlement tank the grey water is suitable for subsurface irrigation, where water passes through subsurface perforated pipes which distribute the water to plant roots
It is not suitable to surface irrigation as chemicals with in the water can damage the external parts of the plant.
For more convenient surface irrigation the grey water should typically have undergone secondary treatment, surface irrigation can be carried out via a micro-drips. Simple micro drips are cheaper than all the underground piping required in subsurface irrigation, how ever there is the added cost of secondary treatment.
There are however several considerations that should be made when irrigating using grey water:
-irrigation of vegetables that have contact with the ground (such as potatoes), or those that are likely to be eaten raw (such as lettuce, carrots, and tomatoes), should be avoided leads to direct ingestion
-grey water is generally alkali so should not be applied to plant which prefer acidic conditions
-the system must have a valve to allow grey water to be diverted back to the sewer when it is too wet to go onto the garden, or in the event of inappropriate substances
-Ideally, the area to be irrigated should be at a lower level than the grey water output so that the entire system can be operated by gravity, and thus there is no need for a pump
-Grey water should be used in quantities that can be taken up by the plants and the soil. Excess grey water will flow to the groundwater and may cause contamination
Another way of indirectly reusing grey water is through heat exchangers..
DEFRA hot water use in our homes – for things like
washing, bathing and cooking – is responsible for 35 million tonnes of greenhouse gas emissions each
year: over 5% of total UK greenhouse gas emissions. Water efficiency measures, particularly those
that focus on hot water use, are therefore doubly beneficial, with water as well as greenhouse gas
savings. We must do more to promote these types of water savings which have multiple benefits

14. Potential savings 5 person household using Aquawiser system Money CO2
150 litres per person day = litres pa
30% saving = litres pa
£1.9 per m3 water = £ 156 saved per year
£2000 system will payback in under 13 years
CO2
0.59kg CO2 / m3 of treated water
0.59(kg/m3)* 82.2(m3)* 1.5(leakages) = 63kg of CO2 saved per house hold pa
Minor saving but if multiplied across the country huge potential savings.
look at the potential saving to a typical 5 person house hold using an Aquawiser system mentioned earlier:
According to DEFRA the average person in UK uses 150 litres a day, this equates to 274,000 litres per 5 person house hold per year. Assuming the system does infect save 30% of mains water usage this equates to 82,200 litres or 82.2 m3
Seven trents average price for mains water in 2007 was £1.9 per cubic meter, this works out as a potential saving per house hold of around £150 per year
Giving a £2000 system a pay back time of just under 13 years.
This seems quite a long time for the system to pay for itself, potentially suggesting that the system may only be a valid investment for larger houses or offices using more water and so saving more.
In terms of CO2 savings from the reduced volume of water being processed a figure of 0.59kg/m3 can be taken, calculated by dividing 3.68million tonnes of co2 produced per day in the treatment and supply of potable water across the UK by 17million litres of water processed per day in the UK. Multiplying this by the house hold water savings of 82.2m3 and a correction factor of 1.5 representing the processed water wasted through leakages a value of 63kg of CO2 per household can be produced.
In the grand scheme of things this a very small saving and does not take in to account the carbon footprint associated with installing the system.
Although these calculations are very rough and based on many assumptions they are likely to be in the right ball park.
The water industry emits under 1% of total UK greenhouse gas emissions, but there is a real
risk that this will rise with water demand and more ambitious standards for water quality in the
natural environment

15. Future of grey water reuse
Government targets to reduce mains water usage from 150 to 130 litres per person per day by 2030
Government water efficiency standards for all new homes
Increasing water stress and rising prices will increase feasibility of re use systems
As more people adopt grey water systems government guild lines/ regulations will be needed
The government aim to see a reduction in mains water per person per year from 150 to 130 litres by 2030 and have set water efficiency standards for all new houses. Meaning it is not inconceivable that they will introduce incentives schemes for implementing grey water re use systems in the near future, although there are no such schemes currently under consideration.
grey water recycling systems more economic feasible for typical house holds.
Although currently household grey water systems do not seem particularly viable for a typical domestic house due to Increasing water stress in many regions of the country and rising prices I believe in the near future more people will adopt some form of reuse system. Meaning it is likely that the government will have to introduce stricter guidelines and laws regarding to protect public health as well as the environment.
Several countries have issued regulations and codes for grey water treatment
and reuse, such as the United States of America and Australia

16. Conclusion
UK needs to value water more highly and not inadvertently waste it.
Grey water reuse is an effective method to increase the efficiency of water usage
Although not particularly feasible for the average house it is set to become more popular in the near future.
need for us all to value water and not inadvertently waste it. Wasting water means wasting a resource on which we are dependent and which is limited
in its seasonal and regional availability. It also means wasting the energy required to supply, treat and
distribute the water to where it is used.
This could be helped by Stronger and more consistent water saving messages from Government and other members of the water industry, they should aim to raise awareness and encourage behaviour change.
Grey water reuse can significantly increase the efficiency of water usage with in a building, reducing water bills and generally having a positive effect on the environment.
Although currently not particularly feasible for the average house it is set to become more popular in the near future as increasing demand causes prices to rise.

17. References
WHO pdf
DEFRA /pdf/future-water.pdf
AquaCo
Sloan AQUS greywater-system-to-help-recycle-bathroom-water.php
Bull, J. (2010, 07). The carbon footprint of tap water. Retrieved 02 09, 2011, from oCoCarbon: carbon.com/2010/07/18/the-carbon-footprint-of-tap- water/
No one cares about references

18. Any Questions?