How a holding tank and a septic tank work
A holding tank is a closed tank with no outlet. Everything that goes down the drain stays in it until a pumping contractor pumps it out. The regulations require it to be watertight and to be emptied regularly enough that the wastewater does not overflow, seep into the ground or spread a smell.
A septic tank is a tank with two or more chambers. Solids settle in it, and the settled water flows on to the infiltration system (a filtration field, drains or a sand-and-gravel filter), where the soil treats it. Without an infiltration system, water from a septic tank must not be discharged into the environment. Read more about the field on the page drain field.
Source: Cabinet Regulation No. 384, points 2.3, 3.3, 4.4 and 4.5 (likumi.lv). Checked on 30 October 2026.
Comparison
| Sealed holding tank | Septic tank with a drain field | |
|---|---|---|
| What happens to the water | It all stays in the tank | After settling, it soaks into the ground |
| Pumping | Often, depending on water consumption and volume | Sediment only: in Riga and Ķekava Municipality at least once a year, in Mārupe Municipality 2 times |
| Soil | Doesn't matter | Must be permeable: sand or gravel |
| Groundwater | The tank must be anchored so it can't float up | High groundwater makes infiltration difficult |
| Space | Only the tank and access for a vacuum tanker | The tank, the field and access |
| Electricity | Not needed | Not needed if there is no pump |
| Running costs | High if the house is lived in all year round | Low |
What it costs per year: an example
A family of three; the water meter shows 9 m³ a month, so that's 108 m³ a year.
- Holding tank of 8 m³: 108 ÷ 8 ≈ 14 pumpings a year. At our price for up to 10 m³ (from €110 per visit), that is from about €1,540 a year, plus travel of ~€1/km outside Riga.
- Septic tank of 3 m³: sediment 1–2 times a year according to the municipal minimum, from €75 per visit, so from €75 to €150 a year.
Work out your own figure from your meter: annual consumption divided by the tank's volume gives the number of times a holding tank has to be pumped. If the house is a summer house with low consumption, the costs of a holding tank can be quite small.
Installation: a septic tank including the tank and the installation work costs from €2,200. The price of a holding tank depends on its volume and the amount of work; read more on the page holding tank installation.
When a holding tank is the better or the only choice
- The soil is clayey or dense, and water doesn't soak into it.
- The groundwater is high, and there is no room for a drain field above it.
- The plot is small, or there is a drinking water well nearby.
- A summer house or sauna with very low water consumption.
- A temporary solution, if a connection to the mains sewer is planned in the next few years.
If the soil isn't suitable for a septic tank but constantly pumping out a holding tank is too expensive, the third option is a BIO plant. Read the comparison on the page septic tank or biological treatment plant. Check the site requirements, such as distances to a well and to boundaries, with the local building authority before construction.
The most common mistakes
- A “holding tank” with a hole in the bottom or an overflow into a ditch. It is no longer watertight and doesn't comply with the regulations.
- A septic tank without an infiltration system, from which water runs into a ditch. The regulations don't allow this.
- Old concrete rings, where groundwater seeps in through the joints. The tank fills up faster than you use water.
- A tank that is too small: a holding tank that has to be emptied every other week quickly becomes the biggest household expense.
If the tank fills up fast, look for the causes on the page septic tank fills up fast. Read about replacing an old tank on the page old septic tank replacement.
What to check before you choose
- Water consumption Look at your meter readings for at least a few months.
- Soil Dig a hole or ask your neighbours: sand and gravel are suitable for infiltration, clay is not.
- Groundwater Check the level in spring, when it is at its highest.
- Access The vacuum tanker has to get close enough to the lid; the hose length is limited.
- Registration In towns and villages, both systems must be registered with the municipality. Read more on the page registering a decentralised sewage system.
Sources
- Cabinet Regulation No. 384: definition of a septic tank (point 2.3), holding tanks (point 3.3), infiltration requirement (point 4.4), holding tank watertightness (point 4.5), handover to a pumping contractor (point 5), reporting changes (point 15.2) checked 30 October 2026
- Riga Binding Regulations No. 66: holding tank formula (point 23), septic tank once a year (point 26), removal to treatment plants or reception points (point 22) checked 30 October 2026
- Ķekava Binding Regulations No. 20/2022: holding tank formula (point 7), septic tank once a year (point 9) checked 30 October 2026
- Mārupe Binding Regulations No. 13/2023: holding tank formula (point 31), septic tank 2 times a year (point 37) checked 30 October 2026