Wastewater systems and their maintenance
By law, a cottage must have a wastewater system suitable for the property. On this page, you will find information on different wastewater systems and the types of wastewater they are suitable for. The page also provides an overview of general maintenance tasks for these systems.
General information
By monitoring and regularly maintaining your wastewater system, you can ensure that it operates as intended. This also extends the system’s service life.
Always follow the manufacturer’s operating and maintenance instructions, as only by doing so can you achieve the water treatment result specified by the manufacturer. A description of the wastewater system, as well as the manufacturer’s or installer’s operating and maintenance instructions, must be kept on the property. Upon request, they must be presented to the supervisory authority.
Wastewater systems function with the help of bacteria that break down impurities in wastewater. For this reason, substances that may disrupt bacterial activity must not be poured into the sewer. These include drain cleaners, such as ‘Kodin putkimies’, and other strong chemicals, disinfectants, solvents, paints, medicines, grease and oils.
Greywater is generated in kitchens and washing facilities. Blackwater refers to toilet wastewater. It is recommended to keep blackwater and greywater separate by using a dry toilet instead of a flush toilet, or by conveying toilet wastewater to a holding tank. This allows greywater to be infiltrated into the soil, and only light treatment is required.
Read more:
- Wastewater treatment (vesiensuojelu.fi)(external link, opens in a new window) (in Finnish)
- Wastewater system maintenance and actions in fault situations (vesiensuojelu.fi)(external link, opens in a new window) (in Finnish)
- Guide to on-site wastewater treatment and instructions for self-monitoring and maintenance (vesi.fi)(external link, opens in a new window) (in Finnish)
Dry toilet
A dry toilet – better known as an outhouse – is an excellent option for a cottage. A modern composting toilet starts the decomposition process immediately, making the toilet odourless. The final material to be emptied resembles soil. Other waterless alternatives include evaporating, incinerating and freezing toilets. A dry toilet can be installed either outdoors or inside a building.
The structure of a dry toilet must be watertight. It must be resistant to rainwater, and no urine or other liquid toilet waste must leak into the ground. These liquids contain high levels of nutrients. If the liquids are conveyed to a greywater (washing water) treatment system, they are subject to the same treatment requirements as toilet wastewater. Read more about treatment requirements.
Toilet waste must be composted due to pathogens for at least one year in a watertight composter. Read more about composting.
Dry toilet maintenance
| Task | Responsible party | Frequency |
|---|---|---|
| Emptying and checking the structures and watertightness: Empty the toilet container. Check that the structure is intact and that no liquids are leaking into or out of the toilet. | Owner | When the container is full |
Infiltration well and stone-filled soakaway pit
If the amount of water used is so small that it can be carried to the cottage or sauna, washing water can be infiltrated into the ground in a controlled manner. Infiltration can be enhanced by using an infiltration well or stone-filled soakaway pit. If you have water fixtures such as a shower, washing machine or pressurised hot-water tank, you will need a proper wastewater treatment system.
Read more: Treatment of small amounts of wastewater (vesiensuojelu.fi)(external link, opens in a new window) (in Finnish)
Holding tank
A holding tank is a watertight container in which wastewater is collected before being transported to a wastewater treatment plant. The holding tank should be equipped with an overfill alarm. The emptying interval can be extended by only conveying toilet wastewater to the holding tank.
The holding tank lid must be intact. If the holding tank diameter is over 40 cm, the lid must also be lockable.
Holding tank maintenance
| Task | Responsible party | Frequency |
|---|---|---|
| Monitoring fill level if no alarm system is installed: Monitor the fill level visually or use a blunt measuring stick that will not damage the tank. | Owner | Once a month |
| Emptying | Professional | When the tank is full |
| Checking the condition of the tank: Visually check the tank for any cracks or dents. | Owner | When the tank is emptied |
| Checking alarm system functionality |
Owner and/or professional | Once a year |
|
Checking the structure and watertightness: Fill the tank with water/wastewater up to the inlet pipe. Wait six hours and check that the water level has not dropped. Check that pipe connections are watertight, the inlet pipe is intact and unobstructed, and that no sludge has accumulated at the bottom. | Owner and/or professional | Once every 5 years |
Read more: Wastewater storage in a holding tank (vesi.fi)(external link, opens in a new window) (in Finnish)
Septic tank
Wastewater systems usually require a septic tank as a pre-treatment stage. In the tank, solid matter settles on the bottom and grease rises to the surface. The clarified wastewater is then conveyed to the next treatment stage.
A septic tank alone without a subsequent treatment stage does not meet the requirements of the Environmental Protection Act. In groundwater areas and near water bodies, this type of system must be replaced immediately. In other areas, it must be upgraded during renovation or when installing a flush toilet. Read more about deadlines.
Septic tank maintenance
| Task | Responsible party | Frequency |
|---|---|---|
| Monitoring fill level if no alarm system is installed: Lower a stick wrapped with gauze to the bottom of the tank and rotate it a few times. Emptying is required when the sludge level is within 10 cm of the lower edge of the outlet pipe T-piece. | Owner | Once a month |
| Emptying | Professional | Twice a year; once a year for tanks that treat only washing water |
|
Checking the condition of the tank: Visually check the tank for cracks and that the T-pieces are in a vertical position. After emptying, fill the tank with clean water to prevent grease from entering the next stage of the system. Wait six hours and check that the water level has not dropped. | Owner | When the tank is emptied |
| Checking alarm system functionality | Owner | Once a year |
| Checking the structures and watertightness | Professional | Once every 5 years |
Small treatment plant
Small treatment plants and greywater filters are factory-made systems for treating wastewater. Devices based solely on biological treatment without the addition of chemicals are only suitable for greywater (washing water) treatment, not for toilet wastewater.
To function properly, small treatment plants require regular servicing and maintenance. Maintenance should always be carried out primarily according to the manufacturer’s operating and maintenance instructions.
Small treatment plant maintenance
| Task | Responsible party | Frequency |
|---|---|---|
| Checking the functionality of the process and technology: no strong odours, control unit information is correct, sufficient chemicals are available, treated wastewater is clear, odourless and free of solids, pumps are working and water is flowing, aeration and chemical dosing are functioning properly | Owner | Weekly |
| Sludge settling test: Instructions for performing the test (vesiensuojelu.fi) (in Finnish) | Owner | Once a month |
| Addition of chemicals | Owner | As needed, approximately every 2 months |
| Excess sludge removal: According to the manufacturer’s instructions | Professional | Every 3–4 months |
| Checking and, if needed, cleaning the discharge pipe outlet | Owner | Once a year |
| Checking overfill alarm functionality | Owner | Once a year |
| Servicing by service company | Professional | Once a year |
| Comprehensive servicing and checking structures/watertightness | Professional | Once every 10 years |
Read more: Small treatment plants (vesi.fi)(external link, opens in a new window) (in Finnish)
Soil treatment (soil filtration system and soil infiltration system)
In soil treatment, wastewater is purified as it passes through the soil. Depending on soil conditions, either soil infiltration systems or soil filtration systems are used. In both systems, wastewater is pre-treated in a septic tank and then distributed via a pipe system over a wide area, where it infiltrates through a filtering layer.
In a soil infiltration system, wastewater percolates through soil layers into groundwater. This method is suitable only for naturally permeable soils. In Espoo, it may only be used for greywater (washing water). Read more about soil infiltration systems (vesi.fi)(external link, opens in a new window) (in Finnish).
In a soil filtration system, collection pipes that gather water are installed below the filter layer. From these pipes, the filtered wastewater is conveyed to a discharge point, such as an open ditch. A soil filtration system can also be built in poorly permeable soil. In Espoo, bottom-sealed soil filtration systems can be used to treat both washing and kitchen wastewater as well as toilet wastewater. Read more about soil filtration systems (vesi.fi)(external link, opens in a new window) (in Finnish).
Maintenance of soil filtration and soil infiltration systems
Soil filtration and soil infiltration systems require only minimal maintenance. The most important task is to ensure that no solids or grease from the septic tank enter the filtration field, as they can clog the system. When the filtration layer becomes clogged over time, the soil material must eventually be replaced. It is also important that there are no trees or plants with deep roots near the filtration area.
Maintenance of soil filtration and soil infiltration systems
| Toimenpide | Tekijä | Tiheys |
|---|---|---|
| Task | Responsible party | Frequency |
| Emptying the septic tank and checking watertightness: See under septic tank | Professional | At least twice a year, see under septic tank |
| Checking and cleaning of distribution chamber and flow regulators: Sludge must not accumulate at the bottom of the distribution chamber, as it can quickly clog distribution pipes. | Owner | Twice a year and always when the septic tank is emptied |
| Checking ventilation through the vent pipes and distribution chamber* | Owner | Twice a year |
|
Checking infiltration through the distribution chamber and vent pipes: Water flows evenly into all the pipes. Water does not stand in the pipes or fill them completely. | Owner | Twice a year |
| Checking the position of the pipes: The inlet pipe slopes toward the distribution chamber, and the outlet pipes leave the chamber at the same height so that water is distributed evenly to each pipe. | Owner | Twice a year |
| Checking the collection pipes and chamber (only for soil filtration systems)** | Owner | Twice a year |
Checking ventilation through the vent pipes and distribution chamber*
- Vent pipes are straight and high enough to prevent blockage by snow.
- The pipes have U-shaped ends or caps that stop debris while allowing air to flow into the pipes.
- There is no strong odour even near the vent pipes.
- There is no odour at all more than 10 meters from the vent pipes.
Checking the collection pipes and chamber (only for soil filtration systems)**
- Check that water is not standing in the collection pipes. Standing water usually indicates a blockage.
- The collection pipes should not be completely empty at all times. They should carry approximately the same amount of water as is conveyed into the filter system.
- An excessive amount of water indicates that additional water is entering the system from the surrounding environment, which reduces treatment efficiency.
- Too little water indicates that the filter system is not sufficiently isolated from the surrounding soil. This is especially problematic if toilet wastewater is being treated in the system.
- If the collection pipes are empty but there is water in the infiltration pipes, the filter layer is clogged. In this case, the entire filter system must be replaced.
- Water leaving a properly functioning filter system is clear, colourless, and only mildly odorous at most.
- The discharge pipe from the collection chamber must always remain open and operational.