The AWWA D100 Standard is a set of guidelines put forth by the American Water Works Association for the construction of welded steel water tanks. It has been adopted by the American National Standards Institute as best practices within the industry for designing and building tanks to be used in water systems. If you are looking to have a water tank built, your custom metal fabricators must be familiar with the AWWA D100 Standard to ensure safety and security of the tank.


steel-water-tanksThe first step in designing an AWWA D100 tank is determining its dimensions. Typically tanks are designed based on the intended volume of water that they will be storing. From there, the engineer can figure out the optimal diameter and sidewall height to achieve this goal. AWWA D100 tanks are typically assembled on site, and can be mounted on an oiled sand base, a concrete foundation, or even the roof of a building. The intended location of the tank can have a large impact on the dimensions of the tank being designed.


The AWWA D100 Standard sets forth stringent guidelines for the materials to be used in tank construction. In this case, carbon steel is the primary material for the tank itself. External parts of the tank may be constructed of other approved materials. Industrial welding equipment will be needed to create a sturdy seam in the carbon steel form.


The AWWA D100 Standard includes a number of external factors regarding the tank as well, including a minimum of two manhole cover access points of no less than 24 inches across. In addition, tanks must include proper ventilation from the roof to account for pressure changes during filling and draining. Since most AWWA D100 tanks are utilized by municipalities for storing potable water, it is imperative that these vents are secure enough to prevent contamination from birds, rodents and insects.

On Site Construction

A staircase running up a storage siloSection 10 of the AWWA D100 Standard lays out specific directions for the erection of the tank once all of the pieces have been assembled by the metal fabricator. There is a significant amount of attention paid to industrial welding in this section as each piece is put together. It is important that all foundation and concrete work for the storage tank is done well in advance and is thoroughly prepared for the tank to be permanently placed.

Quality Assurance

Section 11 of the AWWA D100 Standard is a series of field tests to be done on the tank at the time of construction prior to final painting and coating of the tank. These tests must be completed as part of the quality assurance process to guarantee the quality of the tank’s design. Leak tests should be carried on all components and industrial radiography images should be taken to catch any problem areas other tests might miss. One of the biggest concern when building a new water tank is the strength and quality of the industrial welding at each of the carbon steel joints. That is why the AWWA D100 has paid particular attention to the field testing and repair of welds that show signs of weakness. A skilled team will be able to provide high quality welds backed up by radiography to show their strength.

Tank Completion

Once the tank has been fully erected and tested for compliance with all AWWA D100 Standards, a formal report will be written certifying the tank for use. All relevant information about the design and construction process will be provided to the owner of the tank as well for later reference if necessary. The AWWA D100 Standard is designed to work hand in hand with other AWWA and NSF standards for safety. The AWWA has a separate standard laid out for properly disinfecting the tank prior to its first official use. The NSF and ANSI have also identified a number of internal and external coatings that are safe to use in contact with potable water according to the Additives Standards. Further ANSI standards are also applicable for the ladders, walkways, piping and other external components that are not part of the welded construction of the tank itself.

Choosing a custom fabrication shop to build your AWWA D100 tank can be a difficult task. Depending on the size of the tank being constructed they will need to have a shop large enough to handle all of the individual pieces of the tank before they are sent to the final construction site. Industrial fabrication operations will likely have the tools and resources necessary to handle large capacity tanks, as well as having the ability to travel to the final construction site for assembly. This often requires scaffolding and other specialty equipment to be provided by the metal fabricator.

Swanton Welding has the knowledge, the experience, and the sheer facility size to tackle projects that meet AWWA D100 standards.