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Rainwater Utilization Facilities and Equipment

Klaus W. Koenig, Dipl.-Ing.
Fachvereinigung Betriebs- und Regenwassernutzung e.V.
Professional Association for Water Recycling and Rainwater Utilization (NGO/NPO), Germany

Several hundred thousand rainwater utilization installations were installed during the nineties in Germany. The installation components have been continually improved and now rainwater utilization is generally recognized as an advanced, ecological and permanently safe operating system. Rainwater utilization has thus developed into an important strategy for effective rainwater management.

Rainwater quality and areas of application Rainwater can be used in industry in the public sector in the household.

The savings of potable water through the use of rainwater amounts to about 50 % of household consumption. Household activities where potable water savings can be achieved through the utilization of rainwater include:

The quality of the rainwater collected depends directly upon the collection facilities and installation techniques used. Installations that are competently designed, based on technical standards, supply rainwater that can be used for the applications named above without hesitation. Rainwater collected from such installations is, for example, usually of better quality than authorities demand for lakes used for swimming. [Hollaender 1996]

Legal regulations and standards

It is in the public interest to ensure that the potable water system is protected and secure from possible contamination arising from improper house-owners' installations, including the dangers of a return flow from the rainwater pipework. There are legally binding regulations for this contained within the German potable water legislation for this, and the General Conditions of Water Supply that, apart from purely garden water storage without refilling equipment, are to be maintained in all cases. The technical measures for this are defined in DIN 1988. Of especial importance are potable water feeds and the labelling of pipework and extraction points.

The regulations in detail

• No connection may be made between the rainwater system and the potable water system, not even temporarily! The connecting feed from the public potable water supply to the rainwater system may only be made in an open space of at least 20 mm, according to DIN 1988, part 4 !
• For clear identification of surface pipework, self-adhesive coloured tape with the words "no drinking water" or "rainwater" at short intervals, is to be attached. Where the pipework is under plaster, labels must be plastered in at every metre.
• According to DIN 1988, part 2, extraction points for non-potable water (i.e. also for rainwater installations) are to be labelled with the words "no drinking water", or in picture form.

Recommendations Freely accessible extraction points should, despite the labelling, be secured with a socket key or a closable upper part to the valve, to prevent thirsty children from taking water. In addition taps for garden hoses can be installed at heights inaccessible to children. It is recommended that the rainwater utilization installation be checked for the safety and protection of the public potable water supply! A maintenance contract with the plumber or company carrying out the work increases the operational safety of the installation and relieves the operator from his obligation of care. DIN 1988 determines, in Appendix A, to Part 8, that the open outlet for the feed is to be inspected at least once annually. Among other safety items, the spacing of the inlet valve and the overflow is to be checked with a fully opened inlet.

German Standards for installation

The European neighbours of Germany have generally oriented themselves towards experience gained in Germany. The professional association for water recycling and rainwater utilization "fbr", as a non-profit-making and non-governmental organization with headquarters in Darmstadt, provides a vehicle for information exchange. The essential elements, which pertain to the installation and operation of rainwater collection and utilization, are discussed below based on German experience.

Catchment areas and first flush

Only roof areas should be connected for household use. The separation of the initial quantities of water from a rainfall is unnecessary according to investigations made in the area of the City of Stuttgart [Rott, Schlichtig 1994]. The Environmental Ministry of the German Land of Hessen also writes, in an information brochure, that a first flush is unnecessary for non-potable applications in the household; it is also not recommended because of the reduced amount of water collected.

Filtering before the storage

Filtering before the storage cistern is necessary. The choice of the filtering system depends on the construction conditions. Low-maintenance filters with a good filter output and high water flow are preferred.

In Germany it is no longer current practice to install fine filters in the pressure pipe following the storage cistern. Regular cleaning was often forgotten, especially in private houses, leading to disruptions in the system, pump defects and a deterioration of the water quality.

The technical standard in Germany for fine filters in the storage inlet today is:

• Full cross-sectional area throughout in the size of the inlet, so that the drains cannot be blocked if the filter is not cleaned.
• Large filter capacity so that no back pressure occurs in heavy rainfalls, and cleaning does not have to take place more than 4 times per year.
• Filter unit 0,2 - 0m,8 mm (200 - 800 my)

Many filters of this type, when they have a separate outlet for dirt, reject the first flush as a side stream. Only when the fine mesh is completely saturated with water does it have the optimum permeability. But even with very heavy rainfalls, water is drained away when the permeability of the fine mesh is reached. The annual loss on average is about 10%. The mesh should be removed at least once a year and thoroughly cleaned.

Illustration 3-6  Fine filters in the strage inlet.

A second kind of filter that can be used works without loss, but also without self-cleaning. The dirt collects in front of the filter in a separate filter pit, or in the upper part of the cistern. This type of filter is usually used where high rainwater utilization requirements exist under low rainfall conditions.

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