This Old Tank

Date: September 01, 2020

Hydropneumatic tanks are bladderless pressure vessels typically operating below 75 psi (pounds per square inch). Hundreds of aging public water systems in New Hampshire depend on these tanks for pressure and storage; and most hydropneumatic tanks are either of unknown age or older than their estimated design life of 30 years. Many have not been recently inspected, cleaned, or otherwise maintained. When these tanks fail, they usually fail by leaking through highly corroded bottoms – meaning that systems are paying electrical bills to pump the water directly back into the ground, never reaching consumers. Very rarely, hydropneumatic tanks fail by explosion. This happened in Stonington, CT in 2015.

Although the hydropneumatic tank was externally maintained and under normal operating pressure, forensic investigation found that the explosion was caused by internal corrosion and a manufacturing technique using only one-sided welds around the face of the tank.

NHDES strongly recommends that owners and managers of aged tanks contract with certified, professional tank inspectors to comprehensively evaluate their tanks’ interiors and exteriors – perhaps even consider a tank replacement.

NHDES offers community public water systems a 50% Tank Inspection grant up to $4,000 per atmospheric and hydropneumatic tank, with a maximum of $10,000 per water system, to evaluate tank structure and potential for rehabilitation. Applications will be processed subject to availability of funds. Please contact Luis Adorno at or search the NHDES website for Asset Management for Drinking Water and Wastewater.

Alternatively, the annual Drinking Water State Revolving Loan Fund offers community and non-transient, non-profit public water systems low-interest loans for proactive tank replacements, typically when coupled with upgrades of other system infrastructure. Pre-applications are due annually on June 15. For more information, please search the NHDES website for Drinking Water State Revolving Fund.

Finally, DWGB Sanitary Survey inspectors will be citing Significant Deficiencies for poorly maintained or significantly corroded storage tanks of any type as part of our regular Sanitary Survey visits or Site Inspections. Tanks are one of the most critical assets within a water system. Properly maintaining them should be a top priority. Contact Luis Adorno for more information about tanks and maintenance.