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The size of your septic tank is based on how many bedrooms there are in the house, the square footage of the house as well as the number of people living there. Most residential septic tanks range in size from 750 gallons to 1,250 gallons. An average 3-bedroom home, less than 2500 square feet, will probably require a 1000-gallon tank.

Septic systems can have a serious impact on nearby water sources. A septic tank that is too small will fill up quickly and could send wastewater back into the house. Following state regulations will help protect everyone’s health. Having a properly designed system prevents sewage from leaking into the groundwater.

Make sure the person designing your septic system understands all of the state regulations.


How Septic Tanks Work

Septic systems are underground wastewater treatment structures, commonly used in rural areas without centralized sewer systems. They use a combination of nature and proven technology to treat wastewater from household plumbing produced by bathrooms, kitchen drains, and laundry.

A typical septic system consists of a septic tank and a drainfield, or soil absorption field.

The septic tank digests organic matter and separates floatable matter (e.g., oils and grease) and solids from the wastewater. Soil-based systems discharge the liquid (known as effluent) from the septic tank into a series of perforated pipes buried in a leach field, chambers, or other special units designed to slowly release the effluent into the soil.

When the septic tank is maintained correctly, it can serve your home well, generating all the wastewater from your home.


Why Septic Size Matters

When wastewater enters the reservoir, it needs time to separate. Buoyant materials collect at the top, in a layer called “scum.” This will include things like grease, oil, and toilet paper. Dense materials will fall to the bottom in a layer referred to as “sludge.” The partially clarified liquid in the center is called “effluent,” and, once the solids separate from it, it can move onto the next phase, which is typically a leach field.

If your septic tank is too small, it can be easily overwhelmed by several people taking showers or by doing too many loads of laundry. The liquid will try to go out to the leach field before it has had a chance to separate and this can clog the system, as well as pose health risks. The bacterium in the tank also breaks down the sludge, and as much as 50% will be turned into liquid and gases if the reservoir is effective.

If your septic tank is oversized, you will also have issues. A septic tank that is too big will not run well without the proper volume of wastewater running through it. In oversized tanks, there might not be enough liquid to support the necessary bacteria to break down solids effectively.


How to Determine the Correct Size for a Septic Tank


1. Household Size and Water Usage

The most important point to determine what size septic tank is needed is the average volume of wastewater that will be produced for the septic tank to handle. In a septic system only residence, all wastewater ends up at the septic tank unless a separate system for handling greywater is in place.

The septic tank size needed is dependent on the volume of water it can hold, which will be drained into the soil absorption field. In many parts of the United States, the minimum septic tank size permitted is 1,000 gallons. Based on the overall water consumption of your household, the recommended septic tank sizes are as follows.

  • Less than 1,240 gallons a day: a septic tank of 1,900 gallons
  • Less than 900 gallons a day: a septic tank of 1,500 gallons
  • Less than 700 gallons a day: a septic tank of 1,200 gallons
  • Less than 500 gallons a day: a septic tank of 900 gallons

2. Water Conservation Efforts

On the other hand, if your household is committed to water conservation practices, such as installing low-flow fixtures and being mindful of water use, a smaller septic tank might suffice. Water-saving measures can significantly reduce the overall wastewater output, allowing you to downsize the septic tank without compromising efficiency.

3. Bedroom Count and Home Size

A less accurate guide to calculating your tank size is the number of bedrooms in your home or the square footage of the home. For a 1,000-gallon septic tank, how many bedrooms can you have? It is difficult to say because of varying water usage based on your situation. These calculations assume all bedrooms will be occupied and base the estimated water usage on this data. If you live alone in a three-bedroom house, these calculations will be off. The reason for using these calculations is that a new owner may occupy all the bedrooms and the tank must be of an adequate size to handle the load.

Listed here are the recommended tank sizes based on number of bedrooms.

  • One or two bedrooms under 1,500 square feet: 750-gallon tank
  • Three bedrooms under 2,500 square feet: 1,000-gallon tank
  • Four bedrooms under 3,500 square feet: 1,200-gallon tank
  • Five or six bedrooms under 5,500 square feet: 1,500-gallon tank

4. Property Size

We can calculate typical daily water usage based on the number of people living in your home. We can also consider your overall property size to determine a septic tank that would fit well in your available space. If you have a large property, you will need a larger leach field. If you have a small property, you will need a smaller leach field.

5. Soil Permeability

The drain field’s effectiveness in treating effluent depends on the soil’s permeability. Permeability is the soil’s ability to transmit water. This is measured by the texture and structure of the soil. The soils best suited for wastewater treatment are mixtures of sand, silt, and clays referred to as loamy soils. When it comes to the structure, granular soil is ideal for a septic system because it promotes soil separation and internal drainage. Platy, prismatic and massive structure types are not suitable for conventional septic systems.

Soil with high permeability allows for better wastewater absorption and treatment. Conversely, low-permeability soil requires a larger drain field to avoid over-saturation. A percolation test or soil analysis can help determine the soil’s permeability and inform the ideal septic tank size.

6. Local Regulations

Local health departments or environmental agencies usually have specific requirements and regulations for septic systems. These regulations may dictate the minimum and maximum septic tank sizes allowable based on factors like lot size, proximity to water sources, and environmental concerns. It is crucial to comply with these regulations to avoid potential legal issues and ensure the system’s proper functioning.


Other Factors to Consider

Household capacity is the most contributing factor when considering the size of a septic system. However, there are other factors to consider when evaluating whether your septic system is working for your family.

  • Is your home equipped with water-efficient fixtures and appliances?
  • How conscientious is your family about preserving water usage at home?
  • Are your appliances, toilets and sinks working correctly?

The best way to know if your septic system is adequately sized for your family is to contact a professional. At West Coast Sanitation, we are the trusted experts at helping our clients maintain a healthy septic system. If your family grows, it is essential to remember that it will impact how your system operates.


Call West Coast Sanitation Today!

The fact is that many homes and septic systems were not designed to handle the load put on them from modern appliances and modern lifestyles. But, with a little care and awareness, you can manage this impact and help to avoid increased maintenance problems and the need for costly system repairs and replacement.

At West Coast Sanitation, we know that you don’t have time to deal with septic problems. If you think that your system has reached capacity, please give us a call right away. We have professionals ready to answer your questions and get your system working properly again.

Please give us a call at (951) 780-5922 right away. We have professionals ready to answer your questions and get your system working properly again.