A common question asked by people who are new to rain harvesting is how to install a rainwater tank and whether a rain tank requires a prepared foundation base or if it can simply be put on the ground. This is an important question as it ties into the long term stability of both the tank and rain harvesting system. An improper rain tank base can lead to problems, often due to erosion from weather over time. If not set on a prepared foundation, a rain tank can become unbalanced, settling in one direction, or can completely tip over.
An unbalanced tank can cause strain to the tank as well as any connected plumbing, causing leaks or even breakages. A tank that tips over can cause extensive damage to an existing rain harvesting system or to nearby structures if the tank is full of water and the volume is significant – making proper installation important.
Rainwater tanks will be heavy when full of harvested rainwater. Water weighs around 8.34 pounds for every 1 gallon. Considering this, if you have two 1500 gallon rain tanks, that amounts to a collective weight around 25,000 pounds. In another example, if you have eight 275 gallon IBC totes, this amounts to a total weight around 18,000 pounds when full. Perhaps these examples help to demonstrate how and why a good foundation for a rainwater tank is important.
Preparing a foundation area to install a rain tank can be a quick and easy job when knowing what options are available and what is required for the task.
In this Rain Tanks Series post, we provide a detailed overview of the different recommended foundation types and how to prepare them for the different rain tanks and containers often used in rainwater harvesting.
There are 4 foundation options frequently used as an installation base for rainwater tanks. The best option will depend on the type of tank and total storage volume.
Recommended rain harvesting tank foundation options include: (1) concrete, (2) crusher dust, (3) gravel/sand, and (4) soil.
Crusher dust may also be known as or found for sale as crushed rock.
The foundation types are listed above in order by top recommendation and by their ability to provide strength, stability, and reliability.
All water tanks can be set directly on the ground, i.e., soil, for installation. However, installing rain harvesting tanks on the earth may not be recommended long term due to soil changes that can occur over time from weather erosion.
Below we will consider foundation options and recommendations by individual rainwater harvesting tank type.
Standard cylindrical rainwater collection tanks are one of the most used choices in rainwater harvesting practice. Rain tanks are often available with storage volumes from 100 gallons up to 5000 gallons. They provide the largest volume range of the rain tank types reviewed here, and due to this, can be significantly heavy when in use, making a proper base for these tank types important. For example, a 1000 gallon rain tank will weigh over 8000 pounds when filled with water.
Also known as slimline rainwater harvesting tanks, doorway tanks are a popular choice in rain harvesting. Their popularity is due to their rectangular shape and thin design that makes the tank easy to move and capable of passing through doorways and gates to access locations that larger, cylindrical tanks may not be able to reach.
Rainwater doorway tanks are often available with volumes from 100 gallons up to 1000 gallons. Due to their thinner, box-like design, doorway tanks have a slender base with a small footprint. While this means the tank requires less space, it also means the tank is slightly more prone to the risk of tipping or being knocked over.
Short for Intermediate Bulk Container, the IBC tote is a low cost option popular among DIY individuals and unique home projects. The IBC design is box-like in shape and features a built-in pallet-style platform base. This improves an IBC’s overall stability and suitability for placement in many locations and across material types. An IBC is also easy to move should the need arise. For long term rain harvesting systems, preparing, and setting a permanent foundation is recommended.
In DIY applications, many individuals place IBC totes on concrete cinder blocks. Placing an IBC tote on concrete blocks is an acceptable foundation base; simply ensure the ground is flat and level.
Prior to starting work in preparing the foundation for the rain harvesting tank, choose an ideal site on your property. An ideal site may include the following considerations: away from direct sunlight, on higher elevation, not in a low area where water accumulates, not over underground utilities, and away from trees with large roots or that will have them in the future. What considerations are important may vary on your specific needs, tank, and equipment.
Prior to any rain tank foundation preparation, know the diameter or width by length measurements of your container or containers. All foundations must be sized based on the measurement and volume of the tank.
Rule 1) All foundations for tanks less than 1000 gallons are recommended to measure the width by length of the tank plus an extra 4 inches at least on each side.
Rule 2) All foundations for tanks greater than 1000 gallons are recommended to measure the width by length of the tank plus an extra 20 inches at least to each side.
Rule 3) All foundations that will hold multiple tanks with a total volume less than 1000 gallons are recommended to measure the total width by total length of the tanks with 4 inches of space between the tanks plus an extra 4 inches in foundation width and length.
Rule 4) All foundations for multiple tanks with a total volume greater than 1000 gallons are recommended to measure the total width by total length of the tanks with 10 inches of space between the tanks plus an extra 20 inches in foundation width and length.
The following will lay out how to prepare and set the different foundation options for installing a rainwater tank.
To prepare a concrete slab foundation, measure and mark out the foundation area appropriate for the rain tank(s) size to be installed. Dig out the location and remove the soil to a depth around 4 inches. After digging, ensure dig site is compacted and level. Adding a retaining wall is optional. For tanks above 1000 gallons, adding driveway rebar or reinforcement mesh to the concrete is recommended. Prepare concrete mixture according to directions or have pre-made concrete delivered. Fill dig site to ground level with concrete mixture. Ensure surface is smooth and level. Allow at least 48 hours for concrete to set prior to use. After concrete sets, the foundation is ready for use in rainwater tank installation.
To prepare a crusher dust foundation, measure and mark out the foundation area appropriate for the rain tank(s) size to be installed. Dig out the location and remove the soil to a depth around 4 inches. Ensure dig site is compacted and level. Adding a retaining wall is recommended to help prevent erosion and loss of foundation material. Order crusher dust for delivery or pick up from a landscape supply or nursery. Fill dig site with crusher dust, compact, level, and repeat as needed to ensure foundation is solid, flat, and level. Foundation is now ready for use in rain tank setting and installation.
To prepare a pea gravel and sand foundation, measure and mark out the foundation area appropriate for the rain tank(s) size to be installed. Dig out the location and remove the soil to a depth around 4 inches. Ensure dig site is compacted and level. Adding a retaining wall is recommended to help prevent erosion and loss of foundation material. Order pea gravel and sand mix for delivery or pick up from a landscape supply or nursery. Use pea gravel mixture described as having gravel no larger than 1 ½ inch and with half the mixture smaller than ¼ inch. Fill dig site with pea gravel and sand mixture, compact, level, and repeat as needed to ensure foundation is solid, flat, and level. Foundation is ready for use in rainwater tank setting and installation.
Prepare a soil foundation the same as the other foundation types. Measure out the area, dig up the soil area, and uniformly compact to create a solid, level surface. Foundation is ready for use.
Preparing a proper foundation base for a rainwater tank is ideal to ensure the long-term safety, stability and use of a rain tank for rainwater harvesting. Using a set foundation eliminates the concern of future problems with tank movement, tipping, or unbalancing due to weather erosion. Concrete slabs are the best option for all tank types and volumes but require the most work and cost in preparing. All foundation types must be greater in size than the tank they will support, be solid, and level. In all scenarios, the tank’s overflow plumbing should be routed to discharge excess water off and away from the foundation.
For more on the parts and equipment used in rainwater harvesting, see our post Components of a Successful Rainwater Harvesting System.
If you want to review the rainwater products we have for sale, we offer ANSI/NSF 61 certified rainwater collection tanks here and rain harvesting accessories here. For more information or any assistance, contact us, our professional support staff is always ready to help.
Alek Eccles is a technical writer and professional content creator. Education in english and science; experience in chemical storage, standards; pharmaceutics; environmental assessment and stewardship; governmental regulations and codes. Alek seeks to bring increased understanding to technical, chemical, and biological industries, systems, and concepts; rainwater harvesting; plastics/thermoplastics; as well as containers used for general storage, handling, and transport.
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