If you are planning a construction project away from a municipal area, you will most likely need to include plans for a septic tank and field lines. The location and number of field lines will be determined by the percolation test (sometimes called a perc or perk test) and local codes. The size of the septic tank can be based on water usage or home size.

Calculation by Water Usage

There are a number of methods of calculations to determine the size tank required or needed for your home. The most accurate and reliable way is with water usage. The size of the septic tank required is based on the amount of water it will handle and in turn will be dispersed into the field lines. It should be noted that in many parts of the country, the minimum size tank allowed is 1,000 gallons. Based on the total water usage of your home, the following is a recommended tank size.

Up to 500 gallons per day: 900 gallon tank Up to 700 gallons per day: 1,200 gallon tank Up to 900 gallons per day: 1,500 gallon tank Up to 1,240 gallons per day: 1,900 gallon tank

Calculations By House Size

A less accurate guide to calculating your tank size is the number of bedrooms in your home. 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 reasoning 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: 750 gallon tank Three bedroom: 1,000 gallon tank Four bedrooms: 1,200 gallon tank Five or six bedrooms: 1,500 gallon tank

Estimated Cost

As with any materials or services, the cost can vary widely depending on where you live and the market conditions. For planning purposes we will assume you are planning to use a concrete septic tank. These are by far the most common and have a long life expectancy. The average 1,000 gallon septic tank will cost you between $500 and $700. If you want to move up to a 1,250 gallon tank, you should expect to pay at least an additional $100. If the tank is properly sized you can expect to need to clean it out every three to five years. On average, it will cost you between $75 and $150 to have your tank emptied.