ENGREF Centre De Montpellieroffice International De L Eau

TECHNICAL SYNTHESIS

Rainwater Reuse in the Urban Environment

PERRAUD Audrey

E-mail:

December 2005

ENGREF Centre de MontpellierOffice International de l’Eau

B.P.44494 – 15 rue Edouard Chamberland

34093 MONTPELLIER CEDEX 587 650 LIMOGES

Tél. (33) 4 67 04 71 00Tél. (33) 05 55 11 47 47

Fax (33) 4 67 04 71 01Fax (33) 05 55 11 47 48

Introduction:

The reduction in fresh water resources encourages us to consider the possibility of using poorer quality water for uses not requiring “drinkable” water :the scarcity of water forces us to avoid waste.

In addition, the control of precipitation in the urban environment, imposed by article 35 of the 1992 French Law on Water, can be dealt with by the temporary storage of rainwater.

This is why rainwater reuse has two potential benefits : saving drinking water and limiting the quantity of rainwater entering water treatment plants

We propose here to make a report on the various possibilities, the techniques used in rainwater recycling in the urban environment, the advantages and drawbacks of such techniques and the future prospects of this approach.

PRESENT SITUATION

O REGULATORY PROVISIONS

The collection and reuse of rainwater are authorized in France

The legal status of rainwater is determined by the French Civil Code.Article 641 of the French Civil Code specifies that “any owner has the right to use and dispose of rainwater which falls on his property”.He can thus collect it for his own use, and even sell it (Baralle, 2002).

There are, moreover, obligations related to rainwater (Chéron, 2004) :

-a prohibition to pollute rainwater ;

-an obligation to maintain a “natural” water flow ;

-that rainwater should not inconvenience a neighbourhood.

Rainwater use is subject to rules governing the uses for which this water is intended. In France, the regulations envisage various standards of quality to be respected according to the uses of water (drinking water, bathing water). However, the quality of rainwater does not necessarily satisfy these standards, in particular those related to drinking water which are very strict. Consequently, this water is usable only for certain uses unless it undergoes a particular treatment (Chéron, 2004).

Rainwater can be used for the production of water to be used for human consumption (of a quality known as “drinkable”) according to directive 98/83/EC of November 3, 1998.

The question of the use of rainwater inside households is more complex

As it stands, there is no current specific law regulating the use of water in the habitat and a problem appears on the interpretation of the existing regulatory texts.Indeed, the concept of domestic use introduced in the French Public Health Code concerning water fit for human consumption is interpreted in different ways (Siret, 2005):

• The French Central Department of Health estimates that it includes, in addition to drinking and the preparation of food, many other uses such as dishes, body care, the flushing of toilets, the washing of linen, grounds, vehicles or gardens.In the same way articles 2 and 15 of the standard medical statement provide that rainwater, considered as non-drinkable, can be used only for certain industrial, commercial and agricultural uses not related to food or medical use (Hermann, 2002).

• However, the use of rainwater for toilet flushing happens to be compatible with medical legislation if the use of water for the transport of faeces is not considered as a “medical and food” usage but as a “technical” use.On the other hand, to wash linen with another water than that of public distribution is clearly prohibited.

O CONSEQUENCE: EXTREME CAUTION IS LIMITING RAINWATER REUSE

Because no specific texts exist, the French Central Department of Health and its decentralized services, the DDASS (Departmental Directions of the Medical and Social Affairs), advocates extreme caution (Chesnais, 2004) :the rare operations engaged in this field systematically were only exemptions and in all cases, rainwater reuse requires declarations to the public services (for the personal use of a family;article R.I32I-14) or specific authorizations (article R.I32I-6).

Indeed, the medical authorities consider that it is not desirable to develop non-drinkable water supply networks in collective dwellings, taking into account the risks of interconnections of the networks and convinced that the use of this water is more adapted for uses such as garden watering (Siret, 2005).This reluctance was in particular based on the opinion of an expert department, the CSHPF (French Higher Committee of Public Health) (Appendix I).

In the same way, in a publication dated 22/03/2005, the French department of ecology and sustainable development shows the absence of institutional incentives for this practice :“Rainwater can be used for certain uses, the individual being then able to reduce his drinking water consumption.There is thus no obstacle to the storage of this water in a cistern for watering one’s garden for example.[] On the other hand, rainwater reuse can’t be encouraged for domestic uses, for obvious medical reasons. ”

O YET AT THE SAME TIME DEMAND IS GAINING GROUND

Economic and environmental stakes

For a private individual, a community or an industrialist, rainwater reuse has two potential benefits (Paris, 2002) :by the savings in drinking water that it induces, it allows:

water cost reduction

to save the underground water table feeding the distribution network, because freshwater resources are increasingly in demand.

In addition, rainwater recovery, if it becomes widespread, makes it possible to fight against flooding : indeed it prevents rain drainage by sewers which limit :

the overflow of the water treatment plant, waste water then polluting rivers ;

the reduction in plants’ output because of the dilution of wastewater during rainy periods (Bonneau, 2002).

Knowing that our water consumption is on average 200 L per day (125 L for a private individual in a house, 90 in a collective dwelling, and considerably more for factories), it is estimated that between 26 and 44% of domestic needs could be covered by contributions from rainwater (Siret, 2005).

Concerning the financial savings to be made from rainwater reuse, it seems inevitable that these are indeed possible - since various points of the water invoice are proportional to the volume consumed. (Chéron, 2004), studied a simple example in order to compare the costs involved with and without rainwater reuse. A clear advantage for rainwater reuse is highlighted, and savings can be made from the first year. The financial savings then increase with time, and are much greater after the refunding of the loan taken out for the purchase and installation of the system (See Appendix II).

However, in theory the invoicing of collection and water treatment is established on the whole of water consumption, including recovered water : the regulation clearly states this. This part thus remains fixed : so the financial savings would actually only affect 42% of the total invoice. Domestic rainwater reuse would in fact give rise to financial savings only if these initiatives remain marginal or kept for very limited uses such as garden watering.A generalization of this practice would require a complete tariff reorganization for the production and distribution of drinking water firms in order to ensure it’s financing (Allart, 2002).

O RECOURSE TO THE REUSE OF RAINWATER RISING

To begin with, the first systems of rainwater reuse appeared in individual dwellings.Today, demand also comes from local government and collective establishments such as schools… (De Gouvello, 2005).

In individual houses

In spite of the reluctance of the French Public Health services, private individuals can in all simplicity equip their housing with a system of rainwater collection.The increasing demand in this field results in the appearance of complete do-it-yourself devices to recover and reuse rainwater (Reynaud, 2004) :one can be thus be advised and get tanks, cisterns, pumps, filters and even devices to use rainwater for toilet flushing or washing machines.

In the collective dwellings

TheHQE approach participates in the rise of rainwater reuse

The HQE or High Environmental Quality is an approach concerning the conception and construction of buildings (in particular of collective dwellings, but also public, tertiary or industrial buildings) and aiming at respecting the principles of sustainable development.Initiated at the beginning by the Housing Ministry, the HQE approach then was concretised in a foundation, created in 1996.

To carry out a HQE approach, four categories of targets are specified by the foundation :

• “green-construction” (choice of the processes, building materials)

• “green-management” (waste, water, energy management)

• comfort (thermal, olfactive, visual comfort)

• health (air quality , water)

For manufacturers, estimates showed that the generated overcost goes from 5 to 10% compared to a traditional structure.HQE Buildings make it possible to make savings of water and energy, this additional investment is nevertheless profitable :profitability would require 5 to 10 years on average (Chéron, 2004).

In the field of water, the HQE approach consists of different kinds of measures, and in :

-the use of rainwater for toilets, maintenance and watering ;

-the management of storm water (vegetalisation of roofs, parking areas).

The HQE approach is still little developed in France but is progressing and encouraging the development of rainwater collection systems and reuse in collective dwellings.

Example : the headquarters of the Haut-Rhin Banque Populaire, built in 2001. It is the first HQE building registered in the banking field. The building is equipped with a system of rainwater re-use for flushings, the heating network and for other uses such as car washing. It also has solar collectors for the production of hot water and of photovoltaic panels for the lighting of the car park (Gasser, 2002).

All types of buildings are covered

The buildings equipped with rainwater recovery installations are mainly :

School buildings

Houses

Industrial buildings, garages

Public buildings (gymnasia, exhibition areas, greenhouses)

Colleges taking the lead

The development of rainwater collection and re-use in school establishments and particularly ‘colleges’ can be explained by their favorable configuration (de Gouvello, 2003) : a great potential area in respect of collection, bathrooms all in one place, a good relationship between needs and the availability of the resource (they close during the summer holidays when rainfaill is minimal)

Example:the Saint-Exupéry college in Lyon.Located on an almost entirely waterproofed plateau, the basement of the building will contain a 100 m3 water cistern (for flushings, cleaning the grounds) and a basin of 18 m3 will be created outside for the watering of the parks (Ragot, 2003).

Collective dwellings

The CSTB (Scientific and Technical Center of the Building industry) monitors those projects and achievements using rainwater collection and re-use devices. For the moment the initiatives are few but a growing demand in the field of collective dwellings has been assessed :whereas in 2003 forty projects were counted of which twenty were concluded, in 2004 eighty were counted (de Gouvello, 2005).

Example:the project of Nexity in Courbevoie.A building of 97 apartments is being constructed in Courbevoie in the Hauts-de-Seine. It integrates rainwater recovery and re-use for the 124 toilets of the building.Rainwater is collected from the gravelled roof then will be progressively filtered.They will be then directed towards a storage tank of 70m3 located in the basement.The preliminary studies estimated to 1000 m3 on average the rainwater collected per year, which corresponds to the consumption of flushings of a third of the apartments.This device implies an overcost of 8% for the manufacturer. The construction started in January 2005 (Siret, 2005).

Industrialists now coming on board…

For industrialists, rainwater reuse presents two types of benefits (Reynaud, 2005) : financial savings induced by the reduction in drinking water consumption, but also benefits in terms of communication :environmental concerns are growing, sustainable development is appreciated and such choices represent considerable benefit for a company’s image.

In recent years several projects within major firms could be found. Some reuse rainwater for traditional uses (flushing, watering) ; others go further and innovate (Reynaud, 2005) Renault, for example, set up in its Maubeuge factory a rainwater recycling system which permits them to feed production machines. According to the manufacturer, in 2004, the process made it possible to save 71.300 m3 of drinking water.In Orly, the Paris Airport Authority has also saved each year approximately 70 000 m3 by recovering rainwater falling on platforms. Part of this water is used for the production of air-conditioning during the summer. The RATP is studying rainwater collection to fill the future train washing device of trains in Rueil-Malmaison. The firm hopes to save 5.000 m3 of drinking water per year.

The uses for which it is possible to use rainwater in the current context :Certain uses do not require a water whose quality reaches that of water to be drunk by human beings :it is the case for example, according to the International Water Organisation (OIEau), of the watering of parks, the washing of grounds, roads or vehicles, the filling of reserves against fires.A minimum treatment (mechanical filtration for example) can be set up to improve the quality of collected water and to avoid the clogging of the water distribution network (Coudron, 2002).The rainwater storage conditions must make it possible to keep the initial rainwater quality (Hermann, 2002).
The supply of the WC with rainwater imposes the realization of a complete system entirely distinct from the one bringing drinking water (Chéron, 2004).It is compulsory to prevent the rainwater from getting into the drinkable water network.Moreover, water must go through an important treatment :it should be neither aggressive nor corrosive for the equipment and its users, and must be biologically cleani.e. respect the microbiological criteria fixed for water intended for human consumption (Oieau, 2001).
Uses for which it does not seem possible to use rainwater in the current context:The use of rainwater for food (drinking, food preparation) or sanitary ends (cleaning of the body, linen or products and objects to be placed in contact with foodstuffs) does not seem possible according to OIEau :it would indeed be necessary to be able to treat it so that it respects the criteria necessary for the quality of water intended for human consumption.However, at present such a treatment seems difficult to obtain and very expensive in respect of domestic premises.

RAINWATER RECYCLING SYSTEMS IN FRANCE AND ABROAD

O WHAT ALREADY EXISTS

Abroad

These systems are widespread in certain countries : and the following countries can be quoted as examples - Germany, Sweden, Norway, Luxembourg and India.They are even compulsory for new constructions in Belgium and in certain areas with a significant water shortage like Florida, California or the city of Tokyo (Chéron, 2004).

Certain foreign countries go further reusing grey water, that is to say water coming from washing machines, kitchens or showers, and some even reuse waste water after purification.They can be used for flushings, irrigation, industry.It is the case in Japan, in Australia, in Greece, or in Florida and California (Soroczan, 2002).

In the specific case of the reuse of rainwater, water is mostly used for sanitary uses or for the irrigation of cultures. It is seldom employed to produce drinking water. The regulations vary, but generally require particular parameters of water quality or levels of treatment (Soroczan, 2002).

In the United States, rainwater reuse is seldom encouraged or even allowed. Certain States, like Florida and California where there is a strong water shortage, are departures from the rule. The number of rainwater collection systems in the United States and in the American territories is estimated to be 100.000 (Lye, 2002).Different levels of quality or treatment are required for human consumption, water of contact and the uses without contact like irrigation (Soroczan, 2002).

The example of Belgium :campaigns were launched encouraging people to recycle rainwater, those initiatives being stimulated by the authorities.In 2002, a national law imposed that all new construction be equipped with a rainwater collection device for flushings or garden watering (Chéron, 2004).Certain cities in Wallonia and the majority in Flanders give financial aid for the installation of a rainwater collection cistern.It is estimated that Belgium currently has 300.000 cisterns.

The example of Germany :is a pioneer in Europe as regards rainwater reuse.The achievements are numerous, in particular in Berlin.As in France, there is no precise legislation on the subject but here the authorities show a favorable neutrality.The cities have commit themselves for several years now to an alternative management of water.The recycling of rainwater is subsidized to half by one city in five.The objective is that 15% of the buildings use rainwater.The overcost, especially related to the device of storage, was estimated at 2000 € to equip a house with a system providing 40 to 50% of non-drinking water needs for a family of 4.For 10 years, the market of the rainwater reuse in urban environment has exploded:more than 100 manufacturers are currently in the market (FBR divide, 1999) and the leader, Mall-Beton Gmbh, has installed more than 100.000 systems of rainwater collection in the last 10 years.

On the other hand, the Netherlands recently prohibited rainwater recycling in the residential habitat for domestic use.Exemptions can be made but the conditions to respect are very strict.This prohibition follows a national study highlighting many cases of contamination of the drinkable water network per interconnection with the rainwater one.However, this use remains allowed for the tertiary sector (publicly-owned establishments, offices) under strict conditions (Siret, 2005).

In France

For the moment, rainwater collection in France remains quite exceptional (Beaudoin, 2005).The existing installations are located mainly in the north of France (de Gouvello, 2004).

In France, the average precipitation is approximately 700 mm per annum.

Table 1:Distribution of precipitations in France (Source:Leroy-Merlin)

Area / Average pluviometry L/m2/year
North / 634
West / 772
Is / 771
Center / 727
South-west / 858
South-east / 745
Corsica / 558

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Concerning the volume collected for a suburban habitat, it goes from 50 to 70 m3 per year for an impermeable surface of 100 m2.This volume is reached only if the storage capacity is sufficient and is adapted to the conditions and rhythms of use (Chéron, 2004).

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