Short Answer:
An overhead tank is a water storage structure built at a height above ground level, usually supported on columns, and it supplies water using gravity. An underground tank, on the other hand, is constructed below the ground surface and stores water at or below natural ground level.
The main difference lies in their location, purpose, and pressure delivery. Overhead tanks provide natural water pressure due to height, while underground tanks require pumps to distribute water. Overhead tanks are common in homes and buildings, while underground tanks are used where space is limited or for storing large water volumes securely.
Detailed Explanation
Difference Between an Overhead Tank and an Underground Tank
Water storage is essential in every building and infrastructure setup. In civil engineering, two primary types of water storage systems are commonly used — overhead tanks and underground tanks. Both are constructed using reinforced cement concrete (RCC), but their placement, structural design, water delivery method, and application vary significantly.
Understanding the difference between the two helps in selecting the right type based on usage needs, space availability, and water supply requirements.
Overhead Tank
An overhead tank (OHT) is a storage tank constructed on an elevated platform or columns above ground level. It is designed to supply water through the force of gravity to the building or area below. Overhead tanks are typically placed on rooftops or supported by a framework.
Key Features:
- Elevated position provides natural water pressure for distribution.
- Common in residential buildings, schools, and hospitals.
- Constructed in shapes like circular, rectangular, or intze-type.
- Can be single or compartmentalized for storing different types of water (domestic, fire-fighting, etc.).
- Must resist wind loads, seismic loads, and uplift during empty conditions.
- Maintenance is easy as the tank is accessible from the roof.
Underground Tank
An underground tank is a storage structure built below the ground surface. It is used when ground space is limited or when the tank needs to be hidden from view. These tanks store water for domestic, industrial, or firefighting use and require pumps to lift water to distribution points.
Key Features:
- Located beneath the ground, often under driveways, gardens, or basements.
- Needs external pumping system for water supply.
- Requires waterproofing and protection from soil pressure.
- Suitable for large-scale water storage, rainwater harvesting, or sewage treatment.
- Construction must consider earth loads, groundwater pressure, and accessibility.
- Often used in high-rise buildings for initial collection before pumping to overhead tanks.
Major Differences Between Overhead and Underground Tanks
- Location:
- Overhead tank is above ground; underground tank is below ground.
- Water Pressure:
- Overhead tanks use gravity; underground tanks need pumps.
- Structural Design:
- Overhead tanks resist wind and seismic forces; underground tanks resist soil and water pressure.
- Usage:
- Overhead tanks are ideal for daily water use; underground tanks are used for bulk storage or rainwater collection.
- Construction Requirements:
- Underground tanks need waterproofing, soil protection, and access covers; overhead tanks need strong support columns and bracing.
- Maintenance Access:
- Overhead tanks are easier to inspect and clean; underground tanks need more effort for inspection.
- Temperature Influence:
- Underground tanks stay cooler due to earth insulation; overhead tanks are exposed to weather and sunlight.
Conclusion
Overhead tanks and underground tanks differ mainly in their position, method of supplying water, and structural design needs. Overhead tanks use gravity for water flow and are common in buildings, while underground tanks are preferred where space is limited or for large-volume storage. Choosing between them depends on site conditions, water demand, and practical considerations.