A properly sized septic tank not only prevents breakdowns and overflows, but also ensures effective and environmentally friendly wastewater treatment. At Limpiezas Domingo, with over 15 years of experience in cleaning and maintaining septic tanks in Marina Alta and La Safor, we explain how to calculate the ideal capacity based on the number of users and the use of your home.
According to the Ministry for Ecological Transition, a correctly sized facility reduces environmental impact and ensures compliance with health regulations.
Why is it important to calculate the size of the septic tank correctly?
A tank that is too small will fill up quickly, causing odours, leaks or the need for frequent emptying.
On the other hand, an oversized tank can slow down natural decomposition and affect the internal biological process.
In summary: a septic tank of the right size is more efficient, economical and environmentally friendly.
If you have any doubts about the capacity of the current system, you can request an inspection with a CCTV camera. This allows us to detect the actual volume and any possible obstructions without the need for construction work.
Factors influencing volume calculation
🧍♂️ 1. Number of users or permanent residents
This is the main factor. The more people using the dwelling, the greater the capacity of the septic tank should be.
💧 2. Average water consumption per person
In Spain, average domestic consumption is around 150 litres per person per day, although this can vary depending on habits or the time of year.
⏳ 3. Hydraulic retention time
This is the number of days that the water must remain in the tank for the solids to settle. The recommended minimum is 2 days.
🏠 4. Type of dwelling and frequency of use
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Primary residence (daily use).
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Second home or summer house (intermittent use).
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Holiday rental property (intensive use).
Practical formula for calculating ideal capacity
The simplest formula for estimating size is:
Volume (L) = Number of people × 150 litres × 2 days
Practical example:
| Number of persons | Daily consumption (L) | Retention time | Recommended capacity |
|---|---|---|---|
| 2 | 300 | 2 days | 600 L |
| 4 | 600 | 2 days | 1.200 L |
| 6 | 900 | 2 days | 1.800 L |
| 8 | 1.200 | 2 days | 2.400 L |
| 10 | 1.500 | 2 days | 3.000 L |
👉 Professional tip: always add an extra 20% capacity to compensate for peaks in usage or holiday periods.
Standard sizes of domestic septic tanks
In domestic installations, the following approximate sizes are typically used:
| Type of dwelling | Minimum recommended capacity | |
|---|---|---|
| Small (2–3 persons) | 2–3 | 1.000 L |
| Family (4–5 persons) 4-5 | 2.000L | |
| Large (6–8 persons) | 6–8 | 3.000–4.000 L |
| Intensive-use housing | 6-10 5,000 L or more |
⚙️ If the pit includes additional compartments or a filtration system, the volume may vary slightly. In these cases, it is advisable to consult the domestic sanitation regulations of the Valencian Regional Government.
Recommendations before installing or sizing a septic tank
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Assess the terrain.
Soil with low permeability (clay or rock) will require an additional filtration system. -
Consult current regulations.
Septic tanks must comply with UNE-EN 12566 and respect minimum distances from wells and dwellings. -
Use resistant materials.
Reinforced polyethylene or fibreglass pits offer better durability. -
Choose an authorised company.
At Limpiezas Domingo, a company registered in the Biocides Register (0741-CV), we carry out repairs without construction work, emptying and maintenance in accordance with ISO 9001 / 14001 standards. -
Schedule regular maintenance.
Professional cleaning every 1 to 2 years prevents major problems and ensures optimal performance.
Signs that your septic tank is too small
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Frequent overflows or spills.
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Persistent odours even after emptying.
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Stagnant water in the filter well area.
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Need to empty it more than twice a year.
If you notice any of these symptoms, contact Limpiezas Domingo. We can assess the size of the installation, check the ventilation and carry out a professional septic tank emptying service in a single visit.
How much does emptying or servicing cost?
Emptying a septic tank in Marina Alta costs between €150 and €400 on average, depending on its capacity and access to the work site.
At Limpiezas Domingo, we offer 24-hour service and scheduled maintenance, covering:
📍 Dénia, Jávea, Calpe, Benissa, Moraira, Teulada, Ondara, Oliva and Gandía.
In addition, we use tanker trucks and high-pressure equipment to ensure thorough and safe cleaning.
Calculating the optimal size of a septic tank is not complicated, but it is essential.
An adequate volume prevents breakdowns, improves efficiency, and protects the environment.
Always trust companies with experience and environmental certifications.
📞 Do you have any questions? Call us on 672 450 224 or 966 447 070
💧 Over 15 years taking care of domestic sanitation in Marina Alta.
Frequently asked questions
What happens if I install a septic tank that is smaller than necessary?
It will fill up sooner, generate odours, and you will need to empty it more frequently. In addition, it can affect the soil’s filtering system.
How can I tell if my current septic tank has the right capacity?
You can check the volume in the technical specifications or request a camera inspection to assess its actual condition without excavating.
How often is it recommended to empty a septic tank?
It depends on usage, but ideally it should be done every 1 or 2 years to maintain the biological balance of the system.
What products should I not pour into the drain?
Avoid harsh detergents, oils, solvents, or chemicals, as they destroy the bacteria that perform the purification process.
Where can I find the regulations on septic tank installation?
You can find the latest guidelines and technical requirements on the websites of the Valencian Regional Government or MITECO.
