Sodium hypochlorite is a cornerstone of municipal and industrial water treatment. It is effective, scalable, and widely available. Most water treatment operators know exactly how to use it. Far fewer have put the same level of scrutiny on how they are storing it.
That gap matters. Bleach is corrosive and reactive. It degrades over time, accelerated by heat, UV exposure, and contact with incompatible materials. If the tank material is not rated for the chemical, if venting is insufficient, or if secondary containment is not part of the system design, a facility is accepting risk that is entirely avoidable.
For water treatment operators, the question is not just whether a tank holds liquid. It is whether that tank is qualified for the chemical, the environment, and the regulatory expectations of the facility it serves.
Here is what that qualification actually looks like.
Why Sodium Hypochlorite Demands More from Your Tank
Sodium hypochlorite is not a stable chemical. Over time, it decomposes and releases chlorine gas, a process accelerated by heat, light, and contamination from metals or incompatible materials. For storage tanks, that means the material itself is part of the safety system. A tank that allows chemical degradation to accelerate is not just reducing the effectiveness of your treatment chemical. It is creating a potential gas release and disposal problem.
Polyethylene is widely accepted for sodium hypochlorite storage because of its resistance to the chemical’s corrosive properties. But the type of polyethylene matters. Crosslink polyethylene (XLPE) offers stronger chemical resistance and structural integrity than linear polyethylene. For chemical storage applications, XLPE is the appropriate material. Linear polyethylene is better suited to potable water and FDA-compliant applications.
Assmann manufactures tanks in both materials. XLPE is the standard for chemical storage, including sodium hypochlorite. Linear polyethylene is used for potable water applications. That distinction is not incidental. It is the foundation of a correct specification.
NSF Certification: What It Means and Why It Matters for Procurement
If you are specifying tanks for a municipal water treatment facility, NSF certification is often a procurement requirement, and it is always a meaningful indicator of product quality. NSF International evaluates products through independent testing and material analysis. Certification is not self-reported, and it is not one-time. It requires ongoing compliance.
Assmann is the first crosslink tank manufacturer to achieve NSF certification for chemical storage. Their XLPE tanks are certified for sodium hypochlorite, sulfuric acid, sodium hydroxide, and other listed chemicals. That certification comes with the kind of documentation, product testing, and quality control accountability that procurement teams and regulatory bodies expect.
For potable water storage at the same facility, Assmann’s linear polyethylene tanks carry NSF/ANSI Standard 61 certification for drinking water system components. That means Assmann can serve as a single source for both water treatment chemicals and potable water storage. One supplier. Both certifications. One quality management system behind everything.
When evaluating tank suppliers, it is worth asking whether their certification is current, what chemicals it covers, and whether it is independently verified. Those are not difficult questions. The answers tell you a great deal.
Secondary Containment: From Regulatory Requirement to Operational Standard
Secondary containment for sodium hypochlorite storage is often discussed in the context of regulatory compliance. It is worth treating it as an operational standard regardless of what a specific regulation requires.
Bleach spills are reactive events. A fitting failure or tank issue with sodium hypochlorite is not a simple cleanup. It is a neutralization and remediation situation, with potential impacts on adjacent surfaces, drain systems, and anything the chemical contacts before it is contained. Secondary containment systems limit the scope of that event before it escalates.
Assmann’s double wall tanks (IMT series) provide primary and secondary containment in a single integrated unit, from 20 to 8,850 gallons. The inner tank dome overlaps the outer tank sidewall, which prevents rainwater, snow, and external contaminants from entering the containment space. These tanks eliminate the cost and complexity of lined concrete containment while providing reliable protection for outdoor chemical storage.
For larger installations using vertical storage tanks, Assmann’s secondary containment basins (IRD series) are sized to meet and exceed EPA requirements. The tapered design allows for nesting during shipping, which simplifies logistics for facilities managing multiple tank installations.
Construction Quality: Why Manufacturing Process Determines Long-Term Performance
Here is something that does not always make it into a tank specification but should: how the tank was made determines how it performs over the years it is in service.
Assmann uses a low-and-slow rotational molding process. Tanks are manufactured using non-shielded molds, low temperature heat, and gradual air cooling. This approach allows the crosslinking process to complete all the way through the tank wall, resulting in uniform wall thickness throughout. There are no thin spots, no stress concentrations, and no pressure used in the manufacturing process.
Other manufacturers use water cooling or shielded molds to reduce production time. That approach introduces process-related stress into the tank wall and can interrupt the crosslinking process before it completes. For tanks storing sodium hypochlorite, which is both corrosive and reactive, a tank with uneven wall thickness or built-in stress is a liability over a multi-year service life.
Wall thickness also conforms to ASTM D-1998 standards for liquid storage, which provides a baseline for structural performance across varying chemical and environmental conditions.
Getting the Full Specification Right
Selecting tanks for sodium hypochlorite storage is a system-level decision, not a single-component choice. A complete specification covers:
The Right Partner for Water Treatment Storage
Assmann has been manufacturing polyethylene tanks since 1980. Their product engineers work directly with water treatment facilities to specify the right configuration for each application. That process involves asking the right questions, understanding the chemical environment, and arriving at a storage solution that does not need to be revisited.
For water treatment operators evaluating sodium hypochlorite storage, Assmann’s NSF certifications, ISO 9001:2015 quality management system, and a manufacturing process built around doing things the right way make them a logical starting point.
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Quality: First and Forever.