Water

Types of consumption:

The demand for water in buildings usually concerns the following areas:

Drinking water

The preparation of food and direct consumption requires pure Water. This means wide sterility and low loading of health-hazardous substances. Drinking water is essential where it gets directly into contact with the human organism (meals and drinks, dish washing). Quality survey is regulated by law and obligatory for water supplying companies.

Cleaning and washing

Personal hygiene requires water of high quality as contamination by germs means great risks to health, this is especially true for hot water (see Domestic hot water). Furthermore at hospitals, nurseries and foster homes the use of drinking water for cleaning and washing is obligatory.

Drinking water can be abandoned for household washing. An interesting option is the use of rain water.

Flushing and irrigation

Flushing and the irrigation of gardens doesn't require high quality of water. In such cases drinking water generally can be abandoned. Especially flushing holds an enormeous potential for saving. Each flush uses 3 - 10 l of water.

In 2000 the avarage daily consumption of water in Germany was 128 l per person.

A portion of only 3 l is required for eating and drinking. About 97% are used for other purposes.
Fig. 1: Daily water consumption in households of 128 l per person broken down to purposes [1].


The quality

A decisive factor for the quality of water is its hardness. It defines the concentration of the following solved substances: sodium, calcium, chloride, nitrate and carbonate. Those substances exist as ions in water and are chemical solutions of the salts of hydrochloric, nitric and carbonic acid. Carbonic acid plays an important role as its concentration is notedly high. This is due to the good solubility of carbon dioxide in water. The further presence of calcium-ions leads - especially with rising water temperature - to spontenous accumulation of salts and scaly water pipes.

The unit of hardness of water is degree - the ranges are defined as:

Salt accumulation in water pipes can be prevented by phosphate addives. Up to 5 mg/l of phosphate are allowed according to the guidelines of the WHO (WHO = World Health Organization). The result is a partial softening of the water, the calcium-ions remain solved.

Ion exchangers make use of this very principle. Those can be part of a building's drinking water system. Calcium-ions are substituted by sodium-ions, whereby a too high concentration of sodium-ions must be avoided for sanitary reasons. The EU-guidelines codify a sodium-limit of 150 mg/l. The exchangers have to be regenerated after a certain time what can be regarded as a disadvantage. This procedure amounts to highly salt-loaded sullages.

Calcification and consumption of energy

Calcification not only endangers water pipes, it also can damage devices like washing machines. Hard water produces large amounts of lime especially on heating elements. The energy consumption for hot water increases by approximately 10% per millimetre of lime.

Water hardness and consumption of detergent

Hard water leaves lime-stains on tiles, cuttlery and faucets that can only be removed by the use of acid-containing detergents. A considerable part of utilized washing agents is bonded by ions during the washing procedure without any cleaning effect. As a result, the consumption of agents in very hard water increases up to 100% compared to soft water. This leads to pollution and to danger for ground water.


Extraction and consumption of water

The water distributed through public pipeworks is won from superficial and ground water. Extraction out of rivers and wells demands a significant technical effort. Water supply dams can serve as reservoirs in mountainous areas.

All kinds of water extraction have a refinement to reach the necessary drinking water quality in common. Very high consumption of water can lead to lower ground water levels that effect the environment, micro climate and at last the water quality itself.

Public water supply has a considerable share in the over-all drinking water consumption. A great portion of a household's demand can be replaced by water of lower quality. This holds good opportunities for saving. Suitable measures can decrease the over-all consumption of water significantly. Good examples are the use of rain and grey water. Those are state-of-the-art and more and more frequently used because of their economic advantages.

Figure 2: Annual drinking water consumption of 14,7 billion m³ broken down to sectors [4].

Rainwater

Approximately 50% of the household's water demand can be satisfied by rainwater (garden, washing, flush). Suitable areas for water collection are required in addition to a special storage tank. Rainwater commonly is of high quality often reaching drinking water standard.

The collecting area is essential to the water quality. Inclined roofs are preferable, flat roofs according to their larger defilement are less eligible. Courtyards and traffic routes can't contribute to the collection of rain water.

Figure 3: Principle of rain water extraction and use [2].

The use of rainwater has an additional advantage: peaks of runoff water can be decreased as the storage tanks work as buffers. Loads of sewer systems are less as is the demand for their extension. The expense out of public budgets is reduced.

Abb. 4: Regenwasserangebot in Deutschland, Quelle: Deutscher Wetterdienst

Grey water

Grey water is a part of a household's slop which is not contaminated by excrements and citchen sewage. It is supplied out of shower and bath drains, eventually sink and washing machine can be integrated. A water-saving houshold produces approximately 55 l grey water per day and person. This water accrues every day in the same amount and can be used after a special refinement for the following purposes:

Grey water systems require a dedicated pipework for registration and supply. Depending on the desired purpose the water is purified in different kinds of installations. Several manufacturers of such systems guarantee the required hygienic/microbiological water quality needed for steady use. This Quality is defined by the EU-guidelines for bathing water.

Figure 5: Example for the use and purifiing of grey water [3].

Literature / Links

[1] http://www.wnd.shuttle.de/wnd/wendalinum/wasserverbrauch-BRD.htm

[2] www.regenwasser-systeme.de

[3] Nolde, Erwin; Grauwasserrecycling; Ingenieurbüro Nolde & Partner c/o TU Berlin, Arbeitsgruppe Umweltmikrobiologie

[4] Wassernutzung in Deutschland, Bundesverband der deutschen Gas- und Wasserwirtschaft