The main rule: rainwater does not go into a septic tank, a biological treatment plant or the household sewer. We design and build rainwater systems with gullies, chambers and infiltration in Riga and the Riga region.
Why rainwater must not enter the household sewer
- Septic tank or biological treatment plant: the water that rushes in during a downpour washes out the sediment and the activated sludge. Manufacturers such as AUGUST prohibit discharging rainwater, drainage water and pool water into the plant.
- Holding tank: it fills up much faster, and you also pay for pumping out the rainwater.
- Riga's mains sewer: the binding regulations prohibit discharging groundwater, surface water and underground water into it without the service provider's approval.
- In Riga, land drainage laid lower than the cover of the nearest sewer manhole may only be connected with a special non-return valve or a motorised gate valve.
Sources, checked on 30 October 2026: Riga City Council Binding Regulations No. 17 “Binding Regulations on the Operation, Use and Protection of the Riga City Centralised Water Supply and Sewerage System” (points 63.8, 63.9); LBN 223-15 “Sewerage Structures” (points 89, 90); AUGUST AT6–AT50 technical passport.
What a rainwater drainage system consists of
- Rainwater gullies at the downpipes, with a silt trap and a leaf basket so that sand and leaves do not get into the pipes.
- Channel drains with grates by the garage, terrace or driveway, where water runs across the surface.
- Collector: pipes with an even fall and inspection chambers at bends and junctions.
- Discharge point: infiltration, a ditch, a rainwater sewer network or a tank for watering.
LBN 223-15 allows roof downpipes and land drainage to be connected to a rainwater collection chamber. Land drainage lowers the groundwater around the foundations, while the rainwater system collects surface water. They are different systems, and joining them in a shared chamber has to be planned so that a downpour does not push water back into the land drainage.
Where to discharge rainwater
| Solution | When it suits | What to consider |
|---|---|---|
| Infiltration on your own plot (filtration well, infiltration crates) | Sandy soil, low groundwater | In clay soil, water soaks away slowly, so a larger buffer volume is needed; distance from the foundations |
| Ditch | If there is a ditch at the edge of the plot | You need the consent of the ditch owner or manager; the outlet is reinforced against scouring |
| Rainwater sewer network in the street | If there is one | You need the network operator's technical conditions |
| Tank for watering | Garden, greenhouse | The overflow still has to be discharged in one of the ways above |
In clay soil and high groundwater, infiltration often does not work, and then we choose a ditch or a network. For more on soil conditions, see septic tank in clay soil.
How we build it
- Site visit Where water stands, how many downpipes there are and what area of roof and paving, what the soil is like and where the water can be discharged.
- Layout Pipe route, falls, chambers and discharge point; for infiltration, also the volume needed for a downpour.
- Digging and pipes Trench, sand bed, pipes with an even fall and watertight joints.
- Gullies, channels, chambers We install rainwater gullies with silt traps, channel drains and inspection chambers.
- Discharge point Infiltration crates or a filtration well, an outlet to a ditch or a connection to the network.
- Test We check the flow with water, backfill and restore the surface.
If you are building the household sewer at the same time, the same trench can often be used, but the pipes and chambers stay separate.
How much does it cost?
Pipe installation costs from €25/m. We list the gullies, channel drains, chambers and infiltration unit separately in the estimate, as how many you need depends on the area of roof and paving. The price is also affected by the depth, the soil, restoring the surface and the discharge method.