A summer cottage or holiday home differs from a permanently occupied house in one important way — the wastewater load is uneven. At weekends there may be many people in the house, but then the system stands empty for weeks or even months. This must be considered when choosing a treatment plant.
The short answer
Both a biological treatment plant and a septic tank with additional treatment can suit a summer cottage. A biological system treats water more thoroughly, but after a longer break it needs time to resume working. The choice depends on how often and how long the house is used. If in doubt, use our selection guide.
Why the load is different at a summer cottage
- Uneven load. On weekdays the house stands empty, but at weekends there may be more people than in a permanently occupied house.
- Long breaks. Many summer cottages are not used at all in winter.
- Seasonal peaks. Guests, celebrations and a sauna can produce a lot of water in a short time.
How a biological system works with breaks
In a biological system, wastewater is treated by bacteria that need a regular flow of wastewater. If no wastewater flows in for a long time, the amount of bacteria decreases. After you return, the system needs time for the biological process to recover, and during this time treatment quality may be lower.
That is why for a summer cottage it is important to choose a model that the manufacturer has also designed for uneven loads, and to follow the manufacturer’s instructions for operation while you are away.
What to choose: septic tank or biological system?
| Situation | Most suitable solution |
|---|---|
| The house is used only a few weeks a year | Septic tank with additional treatment (e.g. a drainage field), if the soil and local municipal requirements allow it |
| The house is used every weekend from spring to autumn | A biological system suitable for uneven loads |
| The house is used all year round, including winter | A biological system chosen by number of people |
| The cottage is close to a body of water or a drinking water well | A solution with a higher degree of treatment — usually a biological system |
A detailed comparison of both solutions is in the article Septic tank or biological treatment plant?
Choosing capacity for a summer cottage
For a summer cottage, the system is chosen by how many people usually stay in the house at the same time, not by the maximum number of guests on one evening. An oversized system with a small load will work unstably. If large events are rare, the system’s maximum single load is more important than a high daily capacity.
Preparing the system for winter
If you don’t use the cottage in winter, follow the manufacturer’s operating instructions. General recommendations:
- Never empty the tank completely unless the manufacturer says so — high groundwater can push an empty tank out of the ground.
- Make sure the pipes and the system’s lid are protected from frost.
- Find out whether the compressor should be left on or switched off while you are away.
- Before winter, check whether excess sludge needs to be removed.
What to check before buying
- How often and how long the house is used during the year.
- How many people usually stay in the house at the same time.
- Whether the property has a permanent electricity connection.
- What the soil and groundwater level are.
- Where treated water can be discharged and whether there is a well or body of water nearby.
Not sure what suits your summer cottage?
Our selection guide explains step by step how to choose a system by use pattern, number of people and plot.
Frequently asked questions
Won’t a biological system at a summer cottage start to smell?
A correctly chosen and installed system that is used according to the instructions does not cause unpleasant odours. A smell most often indicates problems with ventilation, load or maintenance.
Can the system be switched off when we leave?
That depends on the model. Some manufacturers recommend leaving the compressor on, others have a special away mode. Follow the operating instructions for the specific model.
Can a cottage use just a holding tank?
A holding tank is a permitted solution, but it must be emptied regularly by a sludge removal service. If water use is high, this can cost more than a treatment plant.