What is a Drinking Water Storage Tank
Created on 07.14
What is a Drinking Water Storage Tank?
A drinking water storage tank (commonly referred to as a potable water tank) is a specialized, hygienically sealed engineering structure designed to store treated, purified water intended for human consumption. Unlike general utility or industrial process tanks, a drinking water tank must be constructed entirely from food-grade, non-porous materials that meet strict public health regulations.
The primary purpose of a drinking water storage tank is to provide a secure physical buffer within a municipal, commercial, or residential distribution network. It protects the stored volume from external environmental contaminants—such as bacterial pathogens, insects, stormwater runoff, and organic debris—while maintaining consistent system pressure and delivering vital reserves for peak daily usage and fire suppression.
What Regulatory Certifications Define a Potable Water Tank?
Because water is a natural solvent capable of absorbing trace chemicals over time, the internal surfaces of a drinking water storage tank cannot contain toxic or leachable components. In professional civil engineering and construction, all materials that touch the water must be strictly certified:
● NSF/ANSI/CAN 61: This is the foundational global standard for health effects. It ensures that components like protective coatings, structural panels, sealants, and gaskets do not leach heavy metals or volatile organic compounds (VOCs) into the water supply.
● NSF/ANSI 372: This standard specifically verifies lead-free compliance, mandating that the weighted average lead content of all wetted surfaces does not exceed 0.25%.
● AWWA Standards: The American Water Works Association provides construction-specific guidelines (such as AWWA D103 for bolted steel or D100 for welded steel) governing the structural integrity and design limits of these containment assets.
What Materials Are Used to Build Drinking Water Storage Tanks?
Selecting a tank material depends on the required storage capacity, local environmental conditions, and the available project budget. The three most prevalent options in modern infrastructure include:
Tank Material | Common Capacity Range | Primary Advantage | Maintenance Profile |
Glass-Fused-to-Steel (GFS) | 20,000 to 5,000,000+ Gallons | Chemically inert glass interior prevents rust and scale formation without a plastic liner. | Extremely Low: Never requires interior sandblasting or re-coating over a 50+ year life. |
Food-Grade Polyethylene (HDPE) | 100 to 15,000 Gallons | Seamless, lightweight, and highly cost-effective for residential or small commercial use. | Low: Requires UV-stabilized or dark compounding to block sunlight and prevent algae growth. |
Welded Carbon Steel | 50,000 to 10,000,000+ Gallons | Highly customizable structural shapes; exceptional structural strength for massive volumes. | High: Requires complete interior and exterior epoxy re-coating every 10 to 15 years to stop rust. |
How Do Storage Tanks Maintain Drinking Water Quality?
Simply pumping clean water into a certified tank does not guarantee it will remain safe. Stagnant water naturally degrades. Water asset managers use specific design strategies to counter the two main threats to water quality:
1. Water Age and Residual Disinfectant Decay
If water sits inside a tank for too long, the chlorine or chloramine disinfectant added during treatment naturally dissipates. Without this residual barrier, opportunistic pathogens like Legionella can proliferate. To prevent excessive water age, modern tanks are sized to ensure a complete water turnover cycle occurs every 3 to 5 days.
2. Thermal Stratification
Solar radiation heats the upper layer of water in a tank, while the lower water remains cold and dense. This temperature split creates stagnant zones where bacteria thrive. To combat this, engineers install active hydrodynamic mixing systems that continuously circulate the water, ensuring completely uniform temperature and disinfectant distribution.
Frequently Asked Questions (FAQ)
Q: What is the difference between a greywater tank and a drinking water storage tank?
A: A greywater tank stores recycled, non-potable wastewater from sinks, washing machines, or rain catchment systems, which is only safe for flushing toilets or subsurface irrigation. A drinking water tank stores strictly purified, treated water that is completely safe for drinking, cooking, and showering. The two systems must never be cross-connected.
Q: Why do drinking water storage tanks require air vents?
A: When water is rapidly drawn from a tank, it creates an internal vacuum that can structurally implode the vessel. Conversely, filling the tank forces air out. Potable tanks utilize high-capacity air vents to equalize this pressure. These vents must be equipped with corrosion-proof, fine-mesh screens (typically 24-mesh or finer) to keep out insects, birds, dust, and airborne pathogens.
Q: Can algae grow inside a drinking water storage tank?
A: Algae can only grow if two conditions are met: the presence of algae spores and exposure to light. Drinking water tanks prevent this by utilizing completely opaque walls (such as dark, UV-blocked plastics or solid steel panels) and secure, light-tight access hatches to completely cut off the sunlight required for photosynthesis.
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