If there is only a sink and a toilet with low use, a holding tank is often enough; if there is a shower, a washing machine and a sauna, you need a septic tank with infiltration. A 2 m³ plastic septic tank costs from €800.
Summer house sewage: three options
| Solution | When it suits | What to consider |
|---|---|---|
| Holding tank | Little water, no space for infiltration, high groundwater | Must be pumped out completely; the more water, the more often |
| Septic tank with infiltration | Shower, kitchen, washing machine; sandy soil | Sludge pumping; infiltration needs space |
| Biological wastewater treatment plant (BIO plant) | The house is used all year round | Poorly suited to seasonal use (see below) |
A septic tank for a garden house often has to fit on a narrow plot with little room for a standard drain field. In that case, a compact infiltration system (tunnels or a filtration well) or a holding tank is chosen. How infiltration works: drain field.
Why a BIO plant rarely suits a summer house
The bacteria in a biological treatment plant need a constant supply of food and air. If the house stands empty for weeks, the activated sludge weakens, and after you return the plant treats poorly for a while. A plant that is not used in winter has to be prepared according to the manufacturer's instructions.
If you live in the summer house for most of the year, a BIO plant is possible. See the page biological treatment plants.
Septic tank for a sauna
Sauna water is mostly grey water: from the shower and washing, warm and soapy, but without faeces. However, it comes in a large volume in one evening, so the tank has to take the whole flow of a sauna evening, and it needs infiltration after it.
If the sauna has no toilet and water use is low, a small septic tank and a filtration well are often enough. If the sauna has a toilet or is part of the house, it is connected to the house's septic tank, and the septic tank volume is calculated including the sauna. Sauna water should not simply be let out onto the ground or into a ditch, because it is also domestic wastewater.
- The connection pipe must have a fall so that it drains by itself and does not freeze in winter.
- Soap and grease form a crust in the first chamber of the septic tank, and it is pumped out together with the sludge.
- If the sauna is also used in winter, the tank and pipe are placed below the frost depth or insulated.
In garden communities: access and pumping
Streets in garden communities (allotment associations) are often narrow, with weight limits or locked gates. Position the summer house septic tank or holding tank so that the vacuum tanker can drive up to it; a smaller tanker (up to 4 m³) needs only a narrower road. More details: septic tank pumping in garden communities.
If the summer house has a dry toilet: dry toilet pumping.
How to prepare summer house sewage for winter
- Pump out the septic tank or holding tank in autumn so that it does not overfill in winter and the crust does not freeze.
- Do not leave a plastic tank completely empty where the groundwater is high, as it can be lifted out in spring; after pumping, partly fill it with water.
- If the house is not heated in winter, drain the water supply so that the pipes do not burst.
- Check that the connection pipe has a fall and that no water stands in it.
- Mark the position of the lid so that you can find it under snow.
How much a septic tank for a summer house costs
A 2 m³ plastic septic tank costs from €800, septic tank installation including the tank and the works from €2,200, and pumping up to 4 m³ from €75 (outside Riga + ~€1/km). For a summer house, costs are often reduced by a smaller volume and a shorter connection pipe, but increased by difficult access for machinery.
The full installation process: septic tank installation; the holding tank option: holding tank installation. All prices: prices.
Rules for summer houses
Cabinet Regulation No. 384 applies to decentralised sewage systems in village and city areas, and therefore also to summer houses and garden houses located there. The system must be registered with the municipality, the contents must be handed over to a pumping contractor, and the pumping certificate must be kept for at least two years. The minimum pumping frequency is set by the municipality; in Riga, for a septic tank it is once a year.
Sources: Cabinet Regulation No. 384 of 27.06.2017, points 3, 4.4, 4.5, 5 and 9.1, likumi.lv/ta/id/291947; Riga City Council Binding Regulations No. 66 of 19.12.2018, point 26, likumi.lv/ta/id/304471. Checked on 30 October 2026.