What is an underground rainwater tank?

An underground rainwater tank is a storage container for a rainwater harvesting system. Rainwater runoff from a rooftop collects in the gutters, into the downspouts, and into the tubing connected to the underground tank. An underground tank provides the advantages and disadvantages of being out of sight. Water stored in a rainwater harvesting system is often used for outdoor applications, such as washing cars and watering gardens and lawns, but can also be routed into a home for potable uses.

What are underground tanks used for?

Underground tanks are typically used for the following applications:

• Rainwater harvesting
• Irrigation
• Greywater
• Non-potable household applications
• Drinking water (with appropriate filters in place)

What are underground tanks made of?

The Norwesco tanks listed above are made from high-density polyethylene. This material is a durable, strong, and long-lasting form of plastic that is ideal for storing potable water supplies. This durability can withstand the pressures of underground storage, such as soil movement and pressure on the surface above the tank. Because of its benefits over other types of plastic, polyethylene is commonly used in trash and grocery bags, packaging film, housewares, squeeze bottles, and many other food and household applications.

What size underground tank do I need?

To size a rainwater tank, you must consider the surface area of your roof, the amount of rainfall in your region, and the volume of stored water you use. To determine how much water will be harvested each rainfall, use the following formula:

Roof size (square feet) x rainfall (inches) x 0.623 = harvested water (gallons)

For example, one inch of rainfall on a 2000 square foot roof provides about 1250 gallons of rainwater to a storage tank. The application you use rainwater for will determine the amount you use and, consequently, the size of the tank you should purchase. You will want to purchase a tank that provides enough water for your applications without running out during a normal weather cycle.

Can I store drinking water in a yellow septic tank?

Unlike white Norwesco tanks, yellow Norwesco septic tanks are not designed to store drinking water. Rather, they should be used for septic systems or storing water used in non-potable applications.

Can I drive over an underground water tank?

Underground water tanks should be installed in a location that will never be driven over or parked on top of. Except in special cases, septic tanks are not designed to bear the burden of a vehicle’s weight or shifts in soil caused by a vehicle driving over the tank. Underground tanks can be encased in concrete to allow for more abuse, but this adds significantly to installation costs.

How much maintenance do underground tanks need?

Underground water tanks should be inspected annually, and bacteria sampling should be performed about every six months. Regardless of inspection results, underground water tanks should be cleaned once every year by chlorinating the tank to kill bacteria.

Underground tank owners should keep an eye out for leaks that become evident at the surface above the tank. If you notice abnormally damp ground or pooling water around your tank, you will need to have your tank inspected for leaks.

How long do polyethylene underground water tanks last?

A well-maintained polyethylene underground water tank should last at least 20 years, with many tanks lasting over 30 or even 40 years. Following a regular inspection and cleaning schedule is crucial in elongating the lifespan on your tank.

Can underground tanks store petroleum products?

No, Norwesco water tanks should not be used to store petroleum products. These soften the walls of the tanks and ultimately cause them to fail.

Advantages of underground tanks

When compared to above ground storage tanks, underground tanks provide the following advantages:

• Reduced risk of contamination
• Less prone to theft
• Completely hidden from sight
• Typically larger capacity
• Maintain a consistent temperature
• Safe from most weather-caused damage
• Save space in your yard

Disadvantages of underground tanks

While underground tanks are excellent for rainwater harvesting systems, they possess the following disadvantages:

• More expensive installation and maintenance
• Difficult to access for maintenance
• Not easily relocatable