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The installation of an underground cistern or septic tank is essential for both clean water storage and waste storage. Before you begin your installation, however, you may ask yourself: What is the difference between a cistern and a septic tank? These differences are important to distinguish before you begin work on either a cistern or a septic tank. In this blog, we explore the differences between cisterns versus septic tanks to help you decide which is better for you.

Septic Tanks

Since “septic” is a word that stems from the Greek term for “rotten,” you can imagine that putting anything that people will consume into a septic tank is never a good idea. Septic tanks are designed to hold both gray water and black water—forms of human water waste held underground. Gray water is used water that contains little bacteria but may contain chemicals from cleaning products. This water can be reused. Black water is bacteria-filled wastewater, such as that from your toilets. Some people consider kitchen wastewater to be black water due to the nature of some products washed down a kitchen drain.

Septic tanks will always be filled and often contain a product or bacteria to break down waste. These tanks should be filled during installation to keep the pressure up the entire time. When you’re comparing cistern versus septic systems, you might be surprised to learn that the contents they hold are very different.

Cistern Tanks

On the other hand, cisterns are not for wastewater or sewage. Cistern tanks are designed to hold drinkable, clean water for homes, businesses, or agricultural purposes. They must be FDA approved to hold a consumable product. Cistern tanks are also designed to be filled, drained, and refilled—unlike a septic tank that will always be filled. They can also hold rainwater! Water cisterns can be made of concrete or plastic, though concrete will offer sturdier protection that may even allow you to drive on top of them.

When installing a concrete cistern, be sure to protect the inside with a concrete cistern liner from Royal Liner. Our liners are FDA approved for potable water and offer an extra layer of protection for your drinking water.


Are there any similarities when comparing cisterns versus septic tanks? There are some areas of overlap for both cisterns and septic tanks—mostly in appearance. The most important of the differences between a cistern and a septic tank to remember is the fact that a cistern is FDA approved to hold potable water; a septic tank is not. This means that you should never have drinking water in your septic tank or purchase a clean septic tank for the purpose of holding drinking water. However, a water cistern can be used as a septic tank and can hold wastewater. Knowing these key differences will save you from a swath of plumbing problems.