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Everything You Need to Know About Rainwater Harvesting Storage

This article lays out everything you need to know about rainwater harvesting storage.

A key component of rainwater harvesting is storage. It is the largest part of the system, grabs the most attention (or least, see In-ground), and is usually the most expensive part of a whole-house rainwater harvesting system.

The options are far from limited when it comes to rainwater storage. Here, we’ll discuss the pros and cons, and hopefully, help you choose what type of storage would suit you best.

Rainwater Storage Location

Rainwater harvesting storage is located above ground, below ground, or partially buried. In deciding what storage is best for you, the key factors are cost and aesthetics.

Other factors such as grade, allocated space, and underground geology can be a factor as well.

Above Ground

Above ground storage is a great option for rainwater harvesting. It allows for a wide variety of tank types, including polyethylene, bolted-steel, timber, and bladder. These require the least amount of excavation which can reduce costs dramatically.

The most common reason that above-ground tanks are not selected is aesthetics, however, is that they can be hidden behind trees or placed away from the home.

Many people use quality above ground tanks as features that complement their landscape design.

Partially Buried

This type is a variation in the installation of above-ground tanks, where the tank is placed slightly in the ground, usually going a quarter to halfway up the tank.


Generally, in-ground tanks require a larger footprint. Excavation costs can be significantly increased when rock is encountered. In-ground tanks vary in their load-bearing capacity from riding lawn mowers to cars to semi-trucks.

Because it allows the ability to use the space, this is an attractive option for many rain harvesters.

Rainwater Harvesting Above Ground Storage

Rainwater Storage Types

Polyethylene (Above or Partial)

The advantages of these tanks are cost and availability in many sizes and shapes. They can be connected together with a crossover pipe at the bottom, provided all tanks are on the same elevation, such as three 2,500 gallon tanks which total in 7,500 gallons of water storage. For above ground use, the most common shape is a vertical tank with a round base. These can be NSF certified.

Polyethylene (In-Ground)

Below-grade polyethylene tanks are ribbed to provide weight support. They are available in sizes up to 2,500 gallons. Like above ground polyethylene, they can be connected together to increase total capacity. These can be NSF certified.

Fiberglass (Above or In-Ground)

Fiberglass tanks can be built for maximum load bearing capacity and are extremely durable. They are most commonly used in commercial and industrial applications. They range from 1,000 to 50,000 gallons and can be NSF certified.

Bolted-Steel (Above or Partial)

Bolted steel are available in flat or corrugated steel. They are available with a 30 degree pitched roof or a flat roof. The finishes can be galvanized, powder-coated, epoxy, glass-fused steel, or weathered steel. Steel tanks include a durable food-grade liner that lines the sidewalls and bottom of the tank.

Cedar/Wood (Above)

These tanks can be quite an enhancement to the landscape design with a unique rustic look. Modern wood tanks are built with pine, cedar or cypress wrapped with steel banding. These tanks also use a food-grade liner.

Water Bladder (Above)

Water bladders are made from a strong coated fabric. They have been used for decades by the military for jet fuel storage. They are available with NSF certification. They are available in sizes ranging from 100 gallons to 300,000 gallons. Bladder tanks are available for a small amount of storage in crawl spaces, but bladder storage is generally used in commercial and agriculture application.

Modular Storage (In-ground)

Modular storage is a collection of crates that are sealed in a plastic liner. They provide unlimited options for depth and shape. Modular storage is most commonly used in commercial applications.

Concrete Storage (Above or In-ground)

Concrete tanks are generally not considered a good option for rainwater harvesting, Precast concrete tanks are limited in size and poured concrete tanks are obsolete. If used, concrete tanks should be coated on the inside to protect against deterioration caused by the slightly lower P.H. of rainwater. These tanks are not suitable for potable water.

Storage Concerns

The three primary questions when determining storage for rainwater harvesting are:

  1. Location. Is the footprint and/or elevation suitable?
  2. Looks. Does it meet your goal for aesthetics around the home?
  3. Cost. Does it fit with your budget?

If your curious about the points above, or have additional questions, give us a call! We’re happy to talk through your options.

Quality of Storage

Rainwater storage is not a place to cut corners. There are many other factors to consider, such as freight, installation, and excavation costs. It is also important that the storage system integrates well with conveyance and pumping system. It must also properly accommodate various in-tank components for a successful rainwater harvesting system.

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