The precious liquid

Use rainwater instead of paying sewage fees

Rising prices for drinking water and wastewater – coupled with an increased appreciation for clean water – have led to significantly greater interest in rainwater harvesting systems or private wells in recent years. When does it make sense to supplement an existing water supply with a rainwater harvesting system?

Water is not only a precious commodity, but also an expensive one, especially in Germany, where it costs one to two euros per cubic meter plus sewage fees. Average water consumption is 123 liters per person per day. Most people use only drinking water, which isn't always necessary: ​​A conscious and sustainable approach to rainwater harvesting protects both the environment and your wallet.

The simplest and most sensible use of rainwater is for garden irrigation. As a rule of thumb, up to 20 liters per square meter are used during the 20 summer weeks each year. Those who water with tap water must pay a wastewater fee in addition to the cost of the drinking water, even though no wastewater is produced because the irrigation water seeps into the ground.

Municipalities also charge fees for the discharge of rainwater that cannot seep into the ground from built-up or sealed surfaces and instead enters the public sewer system. For an average single-family home, this amounts to approximately 150 to 200 euros per year. These fees can be avoided if the rainwater remains on the property.

“A rainwater harvesting system with underground cisterns is particularly suitable where it rains frequently but also experiences dry periods,” says Dietmar Sperfeld of the German Association for Rainwater Harvesting and Utilization in Darmstadt. Unlike a standard rain barrel, underground cisterns allow rainwater to be collected year-round. They can typically bridge dry periods of 18 to 25 days.

"The collected water can not only be used to water the garden, but also to flush toilets and operate the washing machine," explains Michael Henze, environmental officer of the Federal Association of Garden and Landscape Construction (BGL). This makes sense: 35 liters of clean drinking water go down the toilet per person per day.

Not only do plants benefit from soft rainwater, but so do laundry and washing machines. And the environment profits from reduced use of detergent and fabric softener. However, anyone wanting to use rainwater from a (subsidized) cistern in their home needs a second piping system to prevent the mixing of domestic and drinking water. The complex installation of an additional piping system is particularly recommended during renovations or new construction.

Is it worth buying?

 Whether it is worthwhile to supplement an existing water supply with a rainwater harvesting system depends on the amount of the municipal (waste)water fees.

A four-person household can replace approximately 40 cubic meters (40,000 liters) of drinking water with rainwater annually; this figure rises to 60 cubic meters if laundry is also done using rainwater. If wastewater fees are also eliminated, this translates to annual savings of 240 to 300 euros.

The relatively high investment costs must be taken into account: Depending on the storage volume, the costs for storage tanks, pipelines, filters and pumps range between 2,000 and 5,000 euros, in addition to the costs for installation and approximately 100 euros in maintenance costs per year.

A more cost-effective alternative to collecting rainwater in a cistern is accessing groundwater through a private well. However, you can't just start digging; such an undertaking must be reported to the local water authority, which can also provide information on the depth at which groundwater can be found. The specific costs for driven or drilled wells depend on the groundwater depth and soil conditions.

An additional advantage for the well owner is that (provided the groundwater level remains constant), they have a year-round supply of water of better quality, regardless of rainfall. The well requires less space than a cistern and can also be easily installed retroactively.

Sources: umweltbundesamt.de, bauen.de, grundfos.com, my-hammer.de, t-online.de, n-tv.de/ratgeber