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Development of Sustainable Water Management System

1.0 Introduction

A regeneration project close to Bedford will see the construction of a hotel and a school, with both intended to be sustainable. Hunt et al. (2006) judge a development’s sustainability based upon its impact upon the local environment, its cost effectiveness, both during and after construction, and also its impact upon society. These factors tend to relate, to varying degrees on different projects, to how sustainable the development’s water usage is. Taking this into account, those designing and building the school and the hotel have put considerable time and effort into ensuring that the project’s water management setup is from the very top of the line.

The following report focuses on the design and implementation of the regeneration project’s water management system, calculating the respective quantities of water required for the school and for the hospital to run effectively and evaluating the alternative green solutions available to ensure efficient use of water in the two buildings. Among the green technologies looked at, consideration will be given to collection, storage and usage of rainwater to supplement the water supply sourced from utilities companies. Recycled grey water will also be discussed as a possible means of saving water. Lastly, the report will look into methods of conserving water, explaining how they would be implemented and how effective they would be if utilised on this particular project.

2.0 Description of the Regeneration Project

The school that is being constructed will be co-ed and will enrol up to 150 students, catering to children between the ages of six and twelve years old. The school will have a staff of sixteen: eight on full-time contracts, two providing maintenance services and the rest working on a part-time basis. The hotel that is being built will consist of fifty double-rooms and will take on four members of staff on a full-time basis. The school’s roof will be made from pitched tiles, taking up approximately 385 m­2, and approximately 600 m2 of smooth surface. The hotel’s roof will also be made from pitched tiles, but with no smooth surface. It will take up approximately 1,200 m2.

3.0 Estimating water requirements for the school and the hotel

In order to come up with a water strategy, the water requirements of the two buildings must first be approximated. Bradford (2007) notes that for different kinds of end users, there are a variety of purposes that water can be used for, giving the example of the dissimilarity in the water usage patterns of domestic users compared with agricultural users.

3.1 Water requirements for the school

The figures in Table 3.1 calculate the school’s overall water consumption as being at 720 m3/year. Figure 3.1 breaks down the school’s water consumption categorically, displaying the main uses to which water is put in terms of quantity. Flushing toilets takes up the largest proportion (36%) of water consumption (see Figure 3.1).

3.2 Water requirements for the hotel

Hunt et al. (2006) note that there is great variation in the use of water at hotels. What consumption patterns there are tend to relate to water usage by the hotel’s guests, the presence or absence of a hotel swimming pool and the hotel’s star rating. As there is insufficient data regarding the hotel’s star rating and water consumption, a water usage estimate of 30 m3/bed space/year is made, as this is displayed in Table 3.2 (Waggett and Arotsky, 2006) to be the typical consumption in hotels without a rating that do not have swimming pools.

With the average requirement of water estimated at 30 m3/bed space/year and with a total of fifty double-rooms, total demand can be approximated to be = 30*50*2 = 3000 m3.

Hotels use their water supply for bathing, flushing toilets, drinking, cooking, cleaning and gardening. With no data available which can be used to break down water usage into its constituent elements, this is estimated using average UK domestic use (see Figure 3.2) and modified UK hotel use, based on single occupants (see Figure 3.2).

4.0 Non-potable water supply options for the school and the hotel

Hastings (2006) differentiates between water that is fit for drinking, known as ‘potable’ water, and ‘non-potable’ water which, while it is not fit for ingestion, may still be utilised to flush toilets, for cleaning vehicles, buildings or clothes (in washing machines) or to irrigate land. While all non-potable water fails to meet the minimum required standards for drinking water, Hastings makes a further distinction between treated non-potable water, known as green water, and untreated non-potable water, referred to as grey water.

4.1 Rainwater harvesting (RH)

The EA (2003) notes that rainwater collection may occur by gathering the water from roofs or from hard surfaces such as roads using down pipes (see Figure A-1 in the Appendix). The rainwater gathered can be utilised for any number of non-potable water uses. An approximation will be made here of the expected rainwater harvest from the two buildings being constructed.

The rainwater harvest’s quality varies with elements from outside, like the amount of leaves or bird droppings contaminating the harvest. The impact of these elements can be lessened with the use of a protective filter to cover the rainwater outlet (Cornwall Energy Efficiency Advice Centre, 2007). The EA (2003) also notes that rainwater is of a good enough standard to not need treatment after it has been collected, before it can be used. The gathered water will be kept in an over-ground plastic tank, with its placement selected so as to minimise bacteria growth in hot weather, while also minimising frost when the weather is cold. Line filters will also be put in place. With the right choice of filter and of placement, bad smells and water discolouration can be lessened.

4.1.1 Determination of the quantity of gatherable rainwater for the hotel and

The school

Accurately calculating the best quantity of gatherable rainwater for the two buildings calls for a plan of the roofs’ ‘catchment areas’ and also for rainfall data relating to the local area (see Figure 4.1)

(covering the previous 20 years)

It is not possible to gather all of the rain that falls on the buildings and transfer it to the plastic container in its entirety. Usually, rainfall harvests lose something in the region of 10%-60% of the water, varying with the kind of roof in question, the ‘drainage coefficient’ of the material it has been made from (see Table 1) and the filter efficiency: always “0.9â€?. It is also possible to lose rainwater if the container it collects in overflows due to heavy rainfall or low water usage (ibid, 2003).

Table 4.1: Drainage coefficient for different roof types

Roof type

Runoff coefficient

Pitched roof tiles

0.75 – 0.9

Flat roof with smooth tiles


Flat roof with gravel layer

0.4 – 0.5

(Source: EA, 2003)

Based on the aforementioned data, it is possible to work out the potential rainfall harvest in a particular location by inputting the data into this formula (EA, 2008):

Q = AAR x TCA x RC x FC

where Q = Annual Gatherable Rainfall (litres)

AAR = Annual Average Rainfall (mm/yr)

TCA = Total Catchment Area (m2)

RC = Runoff Coefficient

FC = Filter Coefficient

1. For the school

As, logically, a larger roof will allow for the collection of a greater quantity of rainwater, it is important to be aware of the roof area.

The roof surface areas and their construction materials are:

Pitched roof tiles 600 m2

Flat roof (smooth surface) 385 m2

According to Table 4.1, the minimum possible RC for pitched roof tiles is 0.75,

while the RC for smooth surface roofs is 0.5

AAR = Annual Average Rainfall (mm/yr) =∑ Average Rainfall (mm) for the 12

Month period illustrated by Figure 4.1

= 573mm

The Annual Collectable Rainfall (litres), Q = ((600 m2 X (573 mm) X 0.75) +

(385 m2 X (573 mm) X 0.5)) X 0.9

= 331,337.25 litres per annum.

= 331.34 m3 per annum.

This is a lower value than that of the predicted total annual water demand for the school.

2. For the hotel

The hotel’s roof area is 1,200 m2, entirely made from pitched roof tiles.

Q = 1,200 X 573 X 0.75 X 0.9

= 464,130 litres per annum

= 464.13 m3per annum.

This value also falls below predicted annual water demand for the hotel.

Table A-1 (see Appendix A) approximates the monthly rainfall harvest for the two buildings, using the aforementioned equation and using the RC of pitched roof tiles.

The figures for the predicted rainfall harvest and the predicted water requirements point to a shortfall in the ability of the rainwater to fulfil the project’s water requirements. However, the rainwater may still play a significant role, perhaps covering the two buildings’ toilet flushing needs, for instance.

4.1.2 Sizing the storage tank in the RH system for the two buildings

The EA (2003) notes that the storage tank’s purchase price is the most expensive element of setting up the RH system and so deciding upon the right size for it is very important. The biggest tank will not necessarily be the most efficient in the long run and so it is important to work out the optimal size, so that the buildings can harvest sufficient rainwater without overspending. The quantity of water that is kept in the tank should ideally approach the quantity that is required to service the two buildings. The choice of tank must account for price, size and a minimum of two water overflows each year, in order to get rid of unwanted objects in the tank-water. The project planners may also want to invest in a first flush device (Well, 2003) to ensure that the initial water flow, which will contain debris that has collected on the roof, does not enter the tank, keeping its contents relatively clean.

The makers and retailers of the rainfall harvest setup will have means of determining the best tank size for the project. In fact, some of them have applications available for visitors to their websites to work out the optimum size for their needs (e.g. Klargester’s Envireau products, available at and these are handy for making an initial estimate of how much they need to spend. It is best for the planners to go on to discuss this choice with experts in this area.

Figure 4.2: Water balance for approximation of rainwater storage capacity

The EA (2003) notes that the capacity needed will vary according to elements including rainfall patterns, catchment areas, demand patterns, retention time, cost of parts and the cost of and access to alternative supplies. The Development Technology Unit (2008) also states that the level of capacity needed will be based upon several elements, such as weather and rain data, roof surface area, RC and data regarding the number of consumers and the amount of water they use on average.

It goes on to suggest several means of setting the size of system parts:

Method 1 – the demand-side approach (see Appendix A).

Method 2 – calculating the size of the tank based on elements such as storage capacity, overflow and drainage (the supply-side approach) (see Appendix A).

Method 3 – computer model (see Appendix A).

The methods differ in terms of how sophisticated and how complex they are. Some of them can easily be undertaken by people without specialist knowledge, whereas some need specialists familiar with complicated software. The major elements contributing to the method selected include:

  • the size and the complexity of the system and its parts
  • the availability of the components that are necessary to operate using a specific method (e.g. computers)
  • the required skills and technical knowledge/training among the practitioners/designers.

Also, according to the EA (2008), tank size tends to be based upon either the capacity required for 18 days or a 5% share of the annual yield (whichever of the two is lower).

This method will be combined with the supply-side method to determine the tank capacity for this project (see Appendix A).

1. Calculating the optimal tank size based upon the predicted rain yield:

The EA (2003) formula for working out the best tank capacity for the rainfall harvest setup is as follows:

Tank capacity (litres) = Roof area (m2) x drainage factor x filter efficiency x annual rainfall (mm) x 0.05

For the school

Optimal tank capacity (litres) = (600* 0.75* 0.9* 573 mm*0.05) +

(385*0.5* 0.9* 573 mm*0.05)

= 16566.86 litres

= 16.57 m3

For the hotel

Optimal tank capacity (litres) = (1,200* 0.75* 0.9* 573 mm*0.05)

= 23206.5 litres

= 23.21 m3

2. Calculating the optimal tank capacity using the idea of holding 18days-

worth of demand:

Collection tank volume = days storage x average daily demand

For the school

The ‘Estimating water demands for the hotel and school’ section and the figures in Chapter 3 show that the overall quantity of water used to flush toilets, irrigate soil and clean is 612 m3 per annum for the school building. This exceeds the estimated annual rainfall harvest. This being the case, the RH tank will provide water for flushing toilet, with the tank storage for 18 days equalling:

(268 m3/365 days)*(18 days)

= 13.22 m3

For the hotel

According to the figures in Chapter 3, the overall average water requirement at the hotel is 3000 m3. The quantity used to flush toilets, irrigate soil and clean amounts to roughly 53% of the hotel’s water requirement: roughly 1590 m2 per annum. This requirement cannot be covered in total by the RH alone. This being the case, the RH will be limited to cleaning and/or irrigating or to flushing toilets. Even within these limitations, there may not be sufficient rainwater for these tasks.

Using the average daily requirement for toilet flushing:

the tank storage = (3000 x 0.35) m3/365days x 18

= 51.79 m3

Using the average daily requirement for cleaning or irrigating:

the tank storage = (3000 x (0.12 + 0.06)) m3/365days x 18

= 26.63 m3

Using the aforementioned EA (2003) data, a smaller size is optimal. This being the case, if the RH is used to flush toilets, the respective tank sizes for the hotel and the school are going to be 23 m3 and 14 m3. If the method of estimation used is the supply-side method (i.e. it is based upon capacity, overflow and drainage (see the tdix A)), the the optimal respective tank sizes for the hotel and the school will be 35 m3recomm3 m3 and 35 m3ing for these figures is represented bycalculations ad A-3 (seein Appendix A)The selection ultimately made may depend on a combination of these methods of calculation, as well as the price of the tankAfter this, th

4.2 Grey water recycling at the school and the hotel

Metcalf and Eddy (1991) refer to two kinds of wastewater. These are grey and black wastewater. Black water has been flushed down toilets, passed through the drainage system and on to treatment plants. Black water is contaminated with more pollutants than grey water.

Grey water accounts for all of the wastewater which has not been used to flush toilets (EA, 2003). It can be treated and then reused for flushing toilets or irrigating soil (Metcalf and Eddy, 1991). Both Waggett (2004) and the EA (2008) refer to grey water from washing machines, kitchen sinks and dishwashers as black wastewater, as it is heavily contaminated and can contain large amounts of grease and food particles.

Figures 3.1 and 3.3 illustrate that the two buildings will produce grey water at the levels of 55% at the hotel and 32% at the school, 32% and al. (2007) nostate thatis typeg is treated usingrequires biologicalnt systems,by followed by sand filters andts, as the water is heavily contaminatedion because of the high levels treatmeused to flush toilets or irrigate soilThis treated water can be used for toilet flushing and grounwash basins were be colltic decreasing would occur. Collecteequires a physting oninfected sandsith disinfection and membranes suct et al, 2006). This treated watd to flushfor toilets flushing.

Figure 4.3: Schematic of the grey water recycling system to be installed

(Source: Birks et al., 2001)

Grey water is of lower quality than harvested rainwater and always needs treatment before it is used; There areinotgenerally recognised official aegulations regarding grey water’s standard of cleanliness before it can be reusedtoPidou et al., 2007) and individual nations decide upon their own minimum quality requirements. Fs it stands, the UK has no official regulations regarding wastewater usageUnfy wain ). Waggett (2004) nostates thahis lack of legislation is a limiting factor to grey and rainwater of the eyd rainf standards have been put forward by a number of organisations, complicating matters for those wishing to make use of these green solutionsThis makes a sufficient specificationt the subject have found that project planners should ideally set up The majority of the studies available conclude that it is best to operat level of of a health risk exists and what forms of water treatment they should make herefore, the level of treatment required. There are some highly detailed research papdocor the water quality standards for non-potable water re and greywatergrey water) wn in Appendix B.

For the project under consideration here, it would probably be best to gather and treat grey water for use in toilet flushingf

Figures 3.2 and 3.3 display the grey water percentages from showers, baths and hand basins as being 28% for the hotel and 2% for the schools As the school produces relatively little grey water, it is probably best not to bother recycling it in the case of this building, for cost effectiveness purposesTrn the scrin it. He hotel pr a significant quantity of grey water, which will be worth reusing. According toTherefore, economically only the greywbe ey water is generallyeopriate technology for community buildings such as schools, libraries, places of worship and community centres�. The health risks associated with This is because of the potential concerns wither, parthildren are likely to be presresponsible for this. cleanliness especially where children are exposed to the water and little greywatergrey watinn technology would no ve in the case ft

According to Waggett (2004), non-potable (grey or RH) water can be utilised for sub-surface irrigation, as long as no spray mechanisms are involved. “Direct reuseâ€? is another option in areas like laundries (e.g. reusing water from the final rinse for the next wash’s first rinse). This application may be included in the hotel’s design and implemented during construction, though many hotels outsource their clothes cleaning services.

recycling shows the methodology for the design of the grey water recycling system.

The hotel’s grey water will provide 80% of its total water requirement for flushing toilets (28% grey water compared to 35% needed for flushing), with potable water or rainwater automatically supplementing the produced rrecyclin collectio only at 2s insufficient tof theile (see Figure 4.1). recycling004) noteshows thatandit is possible wateh be used in one water setup, and while this increases the quantity of water collected from that which could be expected from a simple RH system, it creates a need for a larger tank to store all of the water and for a greater quantity of chemicals with which to treat the water, both of which will be costly for the projectand rainwater in the same watys

5.0 Discussion and quantification of options for water conservation at the development site

Braithwaite (2006) posits that all developments that aim to be sustainable need to contribute positively to society, be sympathetic to their local environment and ensure that they are cost effective. These factors are referred to as the pillars of sustainable development (Hunt and Rogers, 2005). This part of the report evaluates the potential methods for decreasing the buildings’ water requirements in terms of their impact upon the aforementioned pillars of sustainable development.

The cost effectiveness of the options

If less water is required, then less money will be spent on sewage treatment and savings will also be made in terms of spending on water (Otterpohl, 2006). The savings on water will not necessarily be very large, as UK water prices are not high. The savings made by implementing the green technologies would need to be set against the cost of their implementation in order to work out how long it would take for them to financially justify the expenditure.

The necessary predictions of expected usage would be difficult to make, particularly for the school building, which would have very low usage during holiday periods. In the case of the school, grey water would probably not be cost effective (as discussed earlier) and would probably need a very long time to make sufficient savings to cover is not co2003) estimate a 30% saving on water expenditure is needed to justify investment in the reuse of grey water and it is unlikely that this would be achieved at the schoolMoreover, at the se kitchen eyecyclis

Grey water would, however, be cost effective in hotels; especially big hotels with en-suite accommodation, as customers would consume large quantities of water systems afihite bathrooms and powerful showers an expected part of modern hotels, water consumption is actually higher in the newer establishments, making recycling of non-potable water even more relevantUnlike the majoritutilise treated grey water for toilet flushing when it is busy and revert to its main supply when there are few customer, in order to avoid keeping the grey water in their tank for extended periods. This is common practice in countries with low rainfallrefore, greywatergrey water is

The extra setup required to circulate the treated grey water around the hotel would need significant expenditure from those funding the project and this would have to be given serious thought before deciding whether it would pay off in the long term.

Rain harvesting setups are fairly commonplace at UK schools, as the water is considered to be fairly clean and the running costs are not too. With a lot of water used for toilet flushing, there would be a need for a big tank at the school, which could lead to a big saving over. To carry out a similar harvesting operation, the hotel would require both a large harvesting area (on the roof) and sufficient room to keep the tank. This would probably not be workable for most hotels. Establishments with swimming pools might consider harvesting and treating water to use in their pool.

Social costs

The costs to society of these solutions would take the form of problems with their acceptability and/or their reliability (Hunt et al., 2006) (see Appendix C).

Environmental costs

Braithwaite (2006) views sustainability and environmental protection as being more or less the same thing, with an emphasis upon ensuring that the construction and the running of the buildings is not damaging to the local area going forward. To ensure this does not happen, evaluation of the likely negative externalities of the technologies put forward is needed. Water sustainability for the project might be measured in terms of factors such as impact on the climate, biological diversity and resource depletion. While all of these factors have an environmental aspect to them, climate effects can also create problems in economic terms as well as problems for society in general (Hunt et al., 2006).

The recommended technologies need to be beneficial in terms of future sustainability, with emphasis placed on decreasing both the quantity of water that is wasted and the quantity that is obtained from the mains source.

Integrated costs

On most projects, planners would tend to opt for familiar solutions that are known to be effective over new ones which they might perceive as inherently risky and this might be a factor in the selection made here, particularly in the case of the school, given consideration of the involvement of children (Hunt et al., 2006).

As well as the interests of the planners and developers, it is important – perhaps most important – to give consideration to how the solutions would impact upon the people ultimately using the facilities being discussed. With no official standards for the condition required of non-potable water before it can be used, careful planning is needed to make certain that no errors are made that could potentially cause harm to customers or students. Hotels often take the precaution of labelling water sources such as sinks that provide non-potable water. Another precaution, which might be made use of at the school, would be to use quality gpes (EA, 2008).

Prior to selecting one of the options, the project’s planners should assess how efficient they are by looking into both how secure and how durable their supply of water will be (Hunt et al., 2006). With the rainfall system being wholly reliant upon the weather, this is quite an insecure option, as unexpectedly dry weather will significantly harm the effectiveness of the solution. This might put off the planners, particularly in the case of the hotel, with grey water reuse preferred due to its greater regularity of supply, regardless of the changing seasons, climate or weather patterns recyclingal., 2006). Therefore

6.0 Conclusions and recommendations

The report posits an approach to setting up a sustainable system for managing water at a brownfield development site where a hotel and a school are being constructed. The buildings’ water requirements are approximated from information provided from the exercise paper and CIRIA report no. C657. The report also considers two alternatives for green technologies to help ensure that the buildings have a sustainable water supply, namely the harvesting of rainfall and the reuse of grey water from the buildings recyclinglutions would both provide non-potable water, with the rainwater of a higher standard than the grey water, which would require treatment before it could be reintroduced to the water system, even for uses not involving human ingestion supplied from thes or regulations regarding RH or grey water quality in the United Kingdom, it would be best to utilise the water for functions such as sub-surface irrigation or flushingAs there are not agreed wateould provide sufficient water to fully supply these functions, but could still significantly supplement the water provided by the mains supplyIn addition, that all these uses can not be fully coven to analyse poteo, there iscription in order to identify the methods of qurnservation at the school and the hotel, ultimately recommending that.

water produced by grey water treatment and RH should be utilised for toilet flushing, so as to make savings on water costs and sewage fees.

the RH setup is better suited to the school in terms of sustainability, cost effectiveness and viability than the grey water reuse setup and should be implemented at the school with no grey water treatment operation introduced.

grey water and RH setups should be implemented for the hotel, either in a combined system or separately, so as to make savings and improve the hotel’s water sustainability by supplying the establishment’s toilet flushing function.

water costs and sewage fees are fairly cheap, whereas the costs of implementing either of the suggested green solutions are significantly higher, meaning that these technologies are not commonplace in the UK recyclingthe current situation, population growth and environmental changes are likely to create greater water scarcity and make these approaches to the provision of non-potable water far more common, with governments legislating in their support. However, the growi

there is a need for the EA, the government or another relevant organisation to set up official regulations for non-potable water quality in the UK.

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