Cistern vs. Septic Tank: How To Choose the Right System for Your Home

If you’re looking for a new septic system, there can be a lot of options to sift through, especially when most of them just look like big underground tanks. Take a closer look at two of these underground tanks—cisterns and septic tanks— and examine the differences between these popular septic system options to help you find the best one for your home.

What’s the Difference Between a Cistern and a Septic Tank?

Cisterns and septic tanks are both sturdy tanks designed to hold liquids. They’re typically placed underground within a close distance of the house so that wastewater can travel quickly into the tank. 

The primary difference between cisterns and septic tanks is that cisterns are designed to hold drinkable water and need to be emptied and refilled. Septic tanks are meant to hold wastewater and are emptied far less frequently.

Purpose

Although cisterns can be used as a sewage system to hold wastewater, that’s not their primary purpose—they’re mainly used to hold fresh, clean water that can be used for drinking water for a home or business or as fresh water for animals and agriculture. A cistern’s water source is often rainwater. Some people even use rainwater cisterns as an alternative to wells for a drinking water source. 

Septic tanks have one dedicated purpose—holding sewage, specifically two types of wastewater: graywater and blackwater.

Graywater is water that’s been used in your home and may contain things like soaps and cleaning products but is unlikely to contain any large amounts of bacteria. This type of water can be reused for non-drinking purposes like flushing toilets and cleaning cars. 

Blackwater is wastewater that has a high bacteria content. This type of water isn’t safe to reuse without further treatment, like a filtration and cleaning process after it’s removed from your septic tank.

Materials and Location

Most cisterns are most often made up of either concrete or plastic. You can find some made of fiberglass or steel, as well. 

• Plastic cisterns are lighter and easier to transport and may be located above ground to store drinking water. 

• Concrete cisterns are sturdier and are preferred for underground use. 

Some concrete cisterns are even strong enough that you can drive on top of them, which makes it easy to place them almost anywhere on your property.

Septic tanks are usually made from concrete, though they may also include fiberglass. They’re also buried underground. Although they’re sturdy, it’s not recommended to place them anywhere where machinery or vehicles might drive on top of them so you don’t run the risk of costly septic tank repairs. 

Safety Ratings

Since cisterns are most often used to hold water that’s of drinking quality, they’re required to meet FDA regulations for human consumption. Septic tanks only hold wastewater, so the materials used don’t need to meet any consumption standards. 

Construction and Filtration

Since cisterns are designed to hold liquids, they don’t have any extras. A cistern includes:

• A single big tank

• A cistern hole 

• A separate input pipe for sewage, when it’s used for holding waste

• No filtration system

Septic tanks are specifically intended for sewage, so they have a bit more to their makeup. Septic tanks include: 

• Internal compartments to help separate wastewater

• An inflow pipe that opens into the first chamber

• A partition wall that discourages solid waste from flowing into the second compartment

• An outflow pipe, which is protected by a basic filtration system to prevent solids from entering the pipe

• An initial filtration process for sewage so that cleaner liquids can be directed out of the tank and into the environment

• An external leach field that returns the filtered wastewater back into the soil

Internal Pressure

Cisterns are designed to be regularly emptied and refilled, so they’re built with extra reinforcements to handle the changes in pressure. This reinforcement minimizes the risk of any structural failure in the walls.

Septic tanks are intended to stay consistently filled since the filtration system allows for outflow as well as inflow. As a result, they’re not designed for large pressure changes and don’t have the same structural reinforcement as a cistern.

Installation Cost

Cistern systems are simpler to install than septic tanks and therefore generally cost less. Depending on the size, installing a cistern can range from $6,500 to $8,000, with an average of about $7,000.

The cost to install a new septic tank system can range from $3,500 to $12,000, with an average cost of about $8,000. Septic system installation includes the septic tank and the leach field. 

Maintenance

Since septic cisterns don’t have any way for water to exit, they fill up much more quickly than septic tanks. In many cases, cisterns need to be pumped out about once a month, though that can vary by a few weeks, depending on the size of your tank and your home’s water usage. Cistern pumping usually costs between $300 to $600. 

A septic tank requires a little less maintenance and should be pumped out every 3 to 5 years. On average, the cost of pumping a septic tank is about $400, though it can range from $300 to $600. 

Choosing the Right Sewage System for Your Home

Cisterns and septic tanks both offer underground storage for wastewater, and both septic system types tend to be sturdy and reliable. The biggest decision-making factor when choosing between the two sewage systems is the volume of water you produce in your home.

Although septic tanks have a steeper installation cost, they have much lower maintenance fees in the long run. This is because the filtration and outflow system allows the tank to fill up more slowly than cisterns that have no way for wastewater to exit.

If you’re building a sewage containment system for a cottage or weekend home where you only use a little bit of water, cisterns are convenient and affordable. You also don’t need to plan for extra space for a leach field. 

However, if you’re looking for a full-time water treatment system and you live in a home that has multiple water fixtures like taps, toilets, showers, and laundry machines, the costs to constantly empty a cistern can add up quickly. You’re usually better off installing a septic tank that can process wastewater through a drainage system and only needs to be fully pumped every 3 to 5 years. 

No matter which you choose (or if you’re having trouble choosing and need a little help), a local septic tank company near you can handle all types of septic system installations, maintenance, and pumping for both cisterns and septic tanks so you can rest assured your sewage won’t become a problem later on.