As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
Water tanks can be grouped in several ways, but for rainwater storage, the three main types are above-ground tanks, underground tanks, and elevated tanks. The best choice depends on available space, required water pressure, installation difficulty, climate, and how you plan to use the stored water.
1. Above-Ground Water Tanks
Above-ground tanks sit on the ground or on a prepared base. They are the most common choice for home rainwater harvesting.
Examples include:
- Rain barrels
- Polyethylene storage tanks
- IBC totes used for suitable non-potable applications
- Steel rainwater tanks
Above-ground tanks are usually easier to install, inspect, clean, and repair than buried tanks. Their outlets and fittings are also easier to reach.
The base is important. Water is heavy, so a full tank needs firm, level support that can safely carry the load.
Above-ground tanks also need protection from problems such as sunlight, freezing temperatures, insects, and overflowing water. An opaque tank can help limit light inside the tank, which may reduce algae growth.
Best for
Above-ground tanks work well for:
- Garden watering
- Drip irrigation
- Rainwater collection from homes and sheds
- Washing tools or outdoor areas
- Other approved non-potable uses
Non-potable means water that is not intended for drinking.
2. Underground Water Tanks
Underground tanks are designed to be buried below the soil surface.
They are useful when yard space is limited or when the homeowner does not want a large tank visible beside the building. Larger underground cisterns can also store substantial amounts of rainwater.
However, a tank must be specifically designed for burial. A normal above-ground tank can be damaged or collapse under soil pressure if it is buried.
Underground systems also require more planning. Installation may involve:
- Excavation
- A suitable tank base
- Backfilling
- Overflow drainage
- Access for inspection and cleaning
- Pumps and electrical equipment
- Protection from groundwater pressure
Because excavation and buried tanks can create serious safety and structural risks, larger installations may require qualified contractors.
Best for
Underground tanks can make sense when:
- Above-ground space is limited
- A large storage volume is needed
- Appearance is important
- The site can safely support excavation
- A pump will already be part of the system
3. Elevated Water Tanks
An elevated tank is installed higher than the point where the water will be used. Gravity then helps move water through the outlet and piping.
A small rain barrel on a sturdy stand is a simple example. Much larger elevated tanks may require engineered support structures.
Raising a tank does increase water pressure, but a small increase in height does not create the same pressure as a typical household water system. Gravity-fed systems therefore work best when the equipment below can operate at low pressure.
The support structure must safely carry the full tank. Even a modest amount of stored water creates a large structural load. Do not place a large tank on a deck, roof, platform, or homemade tower unless the structure has been confirmed to support the weight.
Best for
Elevated tanks can work well for:
- Gravity-fed garden watering
- Low-pressure drip irrigation
- Small cabin systems
- Situations where reducing pump use is helpful
How the Three Types Compare
| Tank type | Main advantage | Main limitation |
|---|---|---|
| Above-ground | Easy access and simpler installation | Takes up visible space |
| Underground | Saves surface space | More difficult and costly to install or repair |
| Elevated | Can provide gravity-fed flow | Requires a strong, safe support structure |
For many basic home rainwater systems, an above-ground tank is the simplest starting point. Underground tanks become useful when space or storage capacity is the main concern. Elevated tanks are most useful when gravity flow is part of the system design.
Water Tanks Can Also Be Classified by Material
Placement is only one way to describe water tanks. You may also see tanks grouped by what they are made from.
Common materials include:
Plastic or polyethylene
Consider a suitable water storage tank for home use to evaluate storage-surface compatibility with the planned application.
These tanks are lightweight compared with steel or concrete and are widely used for above-ground rainwater storage. The tank must be suitable for its intended installation and water use.
Steel
Steel tanks can provide large storage capacity and are common in some rainwater systems. Their coatings, liners, fittings, and corrosion protection need to match the intended use.
Concrete
Concrete is often used for large cisterns, especially underground systems. These tanks are heavy and usually require more involved site preparation and installation.
The material does not determine whether a tank is safe for drinking-water storage. If water will be used for drinking, the entire collection and treatment system needs to be designed for that purpose.
Choosing the Right Water Tank
Start with how you plan to use the water.
For simple garden watering, an accessible above-ground tank may be enough. A large property with little open space may benefit from an underground cistern. A low-pressure irrigation system may benefit from an elevated tank if the support structure is suitable.
Also consider:
- How much roof runoff is available
- How much water you want to store
- Available installation space
- Tank dimensions and access
- Inlet, outlet, overflow, and drain connections
- Pump requirements
- Freeze conditions
- Cleaning access
- Mosquito and debris control
- Local requirements for rainwater systems
A tank should also have a safe overflow route. Once the tank fills, additional rainwater needs somewhere to go without damaging the building, tank foundation, or surrounding property.
Tank Type Does Not Determine Water Quality
An above-ground, underground, or elevated tank can all hold contaminated water if the collection system is poorly designed or maintained.
Roof runoff can pick up dirt, animal waste, leaves, microorganisms, roofing debris, and other contaminants before it reaches the tank.
A typical rainwater system may therefore include measures such as gutter screens, debris removal, a first-flush device, tank screening, and treatment appropriate for the intended use.
A first-flush device diverts some of the first runoff from a roof, which often contains a higher concentration of accumulated debris.
Stored rainwater should never be assumed safe to drink simply because it looks clear. Drinking-water use requires a suitable collection system, appropriate treatment, ongoing maintenance, current water testing from a qualified laboratory, and compliance with applicable local requirements.
Frequently Asked Questions
What is the most common type of rainwater tank?
Above-ground tanks are commonly used for household rainwater harvesting because they are relatively easy to install, inspect, clean, and connect to gutters and irrigation lines.
Is an underground water tank better than an above-ground tank?
Not necessarily. Underground tanks save surface space but require excavation and are harder to access. Above-ground tanks are usually simpler to install and maintain. The better option depends on the site and intended water use.
Can any water tank be buried?
No. Only tanks specifically designed for underground installation should be buried. Soil and groundwater can place significant pressure on the tank walls.
Does raising a water tank increase pressure?
Yes. Increasing the height of the water above the outlet increases gravity pressure. However, modest tank stands generally provide much less pressure than a typical household plumbing system.
What material is best for a water storage tank?
There is no single best material. Polyethylene, steel, and concrete tanks can all work well when they are designed for the installation, storage volume, climate, and intended water use.
Can rainwater stored in a tank be used for drinking?
Do not assume stored rainwater is drinkable. Drinking-water systems require suitable collection, prefiltration, treatment, maintenance, current laboratory testing, and compliance with applicable health and plumbing requirements.
Should a rainwater tank have an overflow?
Yes. A tank needs a properly planned overflow so excess water can leave safely when the tank is full. The overflow should not create erosion, foundation problems, or uncontrolled flooding.
