Water can seep away if the soil is unsaturated, i.e. not soaked. In addition, water can seep less easily on sloping soils than on straight soils. Because of the slope, more water flows off the ground than drains off.

The percolation of water depends on the soil permeability, i.e. the pore size of the individual soil components. The coarser the soil, the more permeable it becomes, but the lower the cleaning performance of the soil.

This is how a permeable soil, which, for example, is greened, can absorb 40 % of precipitation water and ensure a high level of groundwater recharge. On the other hand, only 10% of rainwater seeps away on built-up areas (streets, houses). In a sealed area, most of the water drains off at the surface and is fed into the rainwater or combined sewer. For this reason, hardly any groundwater is formed on sealed surfaces.

Research question
How clean is dirty water through the floor?

• Container with opening at top and bottom (e.g. yoghurt pot with hole in bottom)
• Rough stones
• Fine stones
• Sand
• Earth
• Grass
• Water
• Collecting containers

Preparation
The yoghurt pot is gradually filled with the above-mentioned soil components in layers (starting with the coarse stones and ending with a layer of grass). The resulting layers should represent the individual soil layers.

After this, a collecting container is placed under the filled yoghurt pot. The collection container corresponds to the groundwater zone in the experiment.

Then water is mixed with a little earth. The water mixture stands for dirty rainwater.

Test performance
The dirty water is slowly emptied into the yoghurt pot with the individual layers of earth.

Experimental observations
The dirty water flows slowly through the individual soil layers and is cleaned and collected in the collection container. The cleaning effect of the soil and the formation of new groundwater becomes clear.

• Natural cleaning function of the floor (filter capacity) is used
• Water quality in rivers and streams increases and wastewater treatment plants are relieved
• Groundwater recharge is pumped
• Bottlenecks in the sewer network in case of rain events are avoided
• Flood runoff is reduced

• Large space requirements (especially problematic in cities)
• Highly polluted rainwater pollutes soils, rivers and streams

Operation principle
Unsecured, partially secured surfaces

• Very good cleaning effect
• Low effort

• Low storage capability
• Large floor space requirement

Operation principle
Trough infiltration, basin infiltration

• Very good cleaning effect
• Low effort

• Increased maintenance costs due to filling up with garbage and garden waste

Operation principle
Shaft infiltration, drain infiltration, pipe infiltration

• Good storage capacity
• Low space requirement
• small restrictions on the use of the property

• No maintenance possibility
• Very low cleaning effect