Menu

Frequently Asked Questions – FAQ

Auszug aus Broschüre Speidel Regenwassernutzung

What potential savings can I make and how cost effective is it?

With a rainwater harvesting system you can save up to 50% of your daily fresh water consumption. This can be up to 70 litres per person per day (considering using the toilet, washing machine, garden watering and car washing). Given the increasingly expensive and complicated treatment of drinking water, the projected doubling of water prices in the coming years is only logical. So a rainwater harvesting system makes sense in two ways: it relieves and protects not only our environment, but also your  finances in the long-term.

What is the split wastewater fee?

Up to now the sewage charges were calculated on the basis of fresh water consumption. If in one year you used, for example, 100 m³ of fresh water, then you had to pay sewage charges for 100 m³. Up to present, rainwater, etc. was disregarded. However, since there are high costs for the treatment of storm water in the sewer system and the wastewater treatment plant, the cost of waste water and rain water will be calculated separately in future (= split fee). The fees for the sewage will continue to be calculated as previously on the basis of the fresh water consumption (= reading the water meter). The scale of fees is regulated differently by local authorities. In most cases, charges can be reduced by using rainwater harvesting systems.

Who benefits from the split wastewater fee?

The split wastewater fee (GAG in German) is conducive to making the person causing the run-off pay for the cost of storm water disposal. It apportions the charges more justly. Families or residents of apartment houses are mostly relieved of the financial burden. Enterprises and institutions with large impermeable surfaces and low fresh water consumption (for example, shopping areas and transport companies) will be charged more heavily than before the introduction of the GAG.

What positive effects will the GAG have?

The split wastewater fee creates financial incentives for re-exposure of paved areas, for rainwater harvesting and stormwater infiltration on site. It also contributes to flood prevention and conservation of wetland habitats. As such it is an instrument of municipal, environmental control. In the second place, its introduction is also an opportunity for the respective municipalities to create a comprehensive approach to ecological stormwater management. These include, for example, bringing ditches back into use and planting hedges on agricultural and forestry land. This reduces the probability of flood events with the associated personal and economic losses.

Are there public grants for rainwater harvesting systems?

In the meantime, the installation of systems for rainwater utilization are being subsidized by some municipalities directly or indirectly as a measure towards active groundwater protection. You can inquire about local funding in the Building and Environmental departments of your municipality.

Which is better – a concrete or a plastic tank?

As opposed to concrete cisterns, due to their lower weight plastic tanks can usually be moved  without heavy equipment and therefore avoid major damage in the excavation pit and in the garden. This is especially important if you are installing a rainwater utilization system in your garden at a later date. Another advantage of a plastic tank is that it is easier to clean, since concrete tanks have rough inner walls where dirt can accumulate more easily. There is also the risk that particles of cement leaching out might pollute the rainwater and in the worst case cause damage to the pump. Calcium secreted from the concrete of the cistern can also actually make the initially lime-free rainwater "hard" and thereby shorten the life of your washing machine.

How does infiltration work?

In the context of stormwater management, besides rainwater utilization, there is also rainwater infiltration. Both systems can be combined, that is connected one after the other. In that case, the water is first collected in a tank and, after reaching the collector capacity, the excess water is fed to the infiltration system. Infiltration is used where no connection to the sewer or receiving water is possible, and moreover to reduce costs for the split wastewater fee. Infiltration can take place, where licence for direct discharge is given, into the earth via dry wells in the ground surrounded by gravel or via so-called soakaway crates. Depending on local regulations, infiltration into an active topsoil layer may be specified. In this case you will have to employ an enhanced swale (trough-trench) system. Inquire about the approved type of infiltration with the Federal State authorities.

How does a detention tank work?

Basically there are two different versions of a detention tank. In the one, an aperture is made in the tank bottom (depending on flow rate in L / s). The complete volume is thus released at a reduced rate into the sewer system. In the second model, the stored water can also be used as raw water for the home and garden. Here, a flow restrictor is installed in the tank that allows the water above the restrictor to flow away at a reduced rate. The water below the outlet restrictor is thus used as raw water.

Why install a detention tank?

More and more municipalities are specifying the use of a stormwater detention tank on private land. The reason is to release rainwater into the public sewer system at a slower rate to relieve the load. There is also the possibility of retaining rainwater and simultaneous using the raw water for use in the home and for watering the garden. Since the introduction of the split wastewater fee, installing a detention tank has not only ecological, but also economic benefits.

What is the situation regarding the hygiene of rainwater for toilets and the washing machine?

Studies have shown that the average bacterial counts found in rain water are far below the standard values for bathing water or food (eg: salads). When using rainwater for toilet flushing, germs do not matter since their number is negligible compared to the main germs found in human faeces. This also applies when washing clothes. Comparing the germ counts of dirty, unwashed laundry with the counts for rainwater, the same ratio exists.

How often does the tank need to be cleaned?

Depending on the preliminary purification of the rain water (filter) the tank should be cleaned every 8-10 years at the earliest. Unfiltered, fine, suspended particles enter the tank, sink to the bottom and form a layer of sediment, which even has a positive effect on water quality (see next question). So cleaning is only carried out after the sediment layer has reached a considerable depth.

What is sediment and how does it work?

The sediment cleans the accumulated water and is therefore just as important as filtering before reaching the tank. Unfiltered, fine, suspended particles enter the tank and sink under their own weight to the bottom of the tank. In the process, dissolved substances also adhere to the suspended matter as it sinks (adsorption) and are also thus removed from the water and deposited in the sediment. This results in clear water of high quality above the sediment. Note, however, that stirring up the sediment layer should be prevented by means of a stilling inlet.

Strict separation of mains drinking water and rainwater

The aim of DIN 1988 is to protect drinking water from contamination. This means that for feeding in drinking water into a rainwater harvesting systems a free-running outlet is to be used. Of course, all Speidel mains water refill systems are fitted with a free-running outlet.

Labelling of pipes and outlets

Tapping points are to be marked so that any time it is clearly visible which tapping points and pipes contain rainwater. For this purpose we offer a labelling kit.