How much wastewater does a building produce?
The first question for any treatment plant is how much wastewater it has to treat each day. Here is how to estimate it for your house, building or project, with the design figures our engineers use.
Almost all the water you use becomes wastewater
Showers, toilets, washing machines, dishes and cooking: nearly every litre of water that enters a home leaves it as wastewater. A common estimate for homes is roughly 100 to 150 litres per person per day, depending on habits and the season.
For a family of five, that is about 600 litres a day, around 18,000 litres a month and more than 200,000 litres a year. In a septic pit, all of it ends up in the ground.
Why plants are sized above the average
A treatment plant must cope with the busiest days, not the average one: mornings and evenings when everyone showers, laundry days, guests and summer visits. So engineers size the plant with a margin above the average daily use. An undersized plant is one of the most common reasons for smells and overflow.
The design figures we use
| Project | Design capacity |
|---|---|
| Apartment building | 1,000 L/day per apartment |
| Villa up to 200 m² | 3,000 L/day |
| Villa above 200 m² | 4,000 L/day |
| Chalets and bungalows | 200 L/day per guest, minimum 2,000 L/day |
| Compound | 1,000 L/day per apartment + 1,000 L/day per building |
| Restaurant | Sized by our engineers (seats, meals, kitchen) |
Three worked examples
- Building with 8 apartments: 8 × 1,000 = 8,000 L/day (8 m³/day).
- Villa of 250 m²: above 200 m², so 4,000 L/day.
- 10 chalets with 4 guests each: 40 guests × 200 L = 8,000 L/day.
From capacity to tank size
Our fiberglass plants are horizontal tanks that hold about one day of flow. Once you know the capacity, the tank length follows from the diameter you choose. For example, 8,000 L/day in a tank of 200 cm diameter needs a length of about 260 cm, with a total height of about 230 cm including the manholes.
A larger diameter gives a shorter, more compact tank, which helps on narrow or sloping plots.
Calculate yours in one minute
Our free Plant Configurator applies these figures to your project and draws the tank with its dimensions. Restaurants, hotels, schools and factories need a few more details: send them to us and an engineer will size the plant.
Not sure you need a plant at all? Read septic pit or treatment plant: which is right for you.
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