A complete technical guide to
galvanized elevated tanks

An elevated tank works on the simple principle of hydrostatic pressure. The water column in the tank creates pressure at its base through its own weight, directly proportional to the height of the column. The basic relation is P = ρ × g × h.

An elevated tank system is made up of the following parts:

The main water-holding vessel, built of bolted panels or welded plate.

The steel or concrete structure that holds the tank at height.

A reinforced concrete foundation that carries the structure's loads to the ground.

Inlet, outlet, overflow and drain lines and control equipment.

Access ladder, inspection platform, safety guards, manway and venting system.

Degreasing: removing oil, grease and organic contamination in an alkaline or acid solution. Pickling: removing rust and mill scale with hydrochloric or sulphuric acid. Fluxing: dipping in zinc ammonium chloride to prevent re-oxidation before immersion. Immersion in molten zinc: dipping the part in a zinc bath at about 440–460 °C, forming the alloy layers. Cooling and inspection: cooling the part and checking coating thickness, continuity and adhesion.

A hot-dip galvanized coating is made of several layers of different composition and hardness. From the steel surface outwards come the gamma, delta and zeta layers — zinc–iron alloys with decreasing iron content — and finally the outer eta layer of pure, ductile zinc. The inner alloy layers are usually harder than the steel itself and give the coating high abrasion resistance.

Barrier protection: the zinc layer is a physical barrier that cuts off moisture and oxygen from the steel. Cathodic/sacrificial protection: if the coating is scratched or locally damaged, zinc — having a more negative electrochemical potential — oxidises before the steel and, acting as a sacrificial anode, prevents the base metal from corroding. This is galvanizing's fundamental advantage over paint.

Coating thickness decides how long galvanizing lasts, and it is set by the thickness of the steel part and the standard's requirements:

The relationship between coating thickness and life is roughly linear; each micron of coating can give years of protection in low to medium corrosivity environments:

Uniform protection over every surface, including edges, corners and hard-to-reach spots that painting usually covers poorly. Long life and a big cut in maintenance cost over the tank's life cycle. High mechanical and abrasion resistance of the alloy layers against knocks and wear during transport and installation. Simple visual inspection: thinning and colour change of the coating are a visible indicator of its protective state.

Here the tank shell is made of steel panels, each hot-dip galvanized separately in the factory under controlled conditions. On site the panels are joined with galvanized bolts and sealing gaskets (such as EPDM sealing strips or polysulphide mastic). Since no welding is done on site, the galvanized coating stays intact and uniform.

Here the steel plates are joined by welding into a continuous shell with no bolted seams. The main challenge is that welding and galvanizing do not mix: if the parts are galvanized before welding, the welding heat burns off the zinc along the seam, which must then be repaired by cold methods (zinc-rich paint or zinc metal spray) that never match the original hot-dip coating. If they are galvanized after welding, the size of the shell makes dipping it in the zinc bath practically impossible.

In rural areas, which often face unreliable power and need low-maintenance solutions, a galvanized elevated tank stores water during low-demand hours and supplies gravity pressure at peak hours, reducing reliance on continuously running pumps and making supply more reliable. The light weight and portability of the panel tank make it economical to build in remote and hard-to-reach areas.

In municipal networks, the elevated tank regulates pressure, balances demand swings and provides emergency storage. During power cuts or pump failures, the stored water can hold network pressure for a while and prevent a sudden loss of service.

Supplying water and pressure for fire-suppression systems in industry and large complexes. Storing process water in industrial and agricultural units. Supplying water to large residential, commercial and agricultural complexes.

Where the galvanized coating has been damaged by an impact or scratch, it should be repaired as soon as possible with zinc-rich paint containing at least 92% zinc in the dry film. Direct contact between galvanized steel and dissimilar metals such as copper must be avoided to prevent galvanic corrosion.

With a standard galvanized coating and proper maintenance, a tank in an ordinary urban environment can last several decades; the exact figure depends on coating thickness and the environment's corrosivity category.

In most projects the bolted panel tank is preferred for its uniform coating, speed, transportability and expandability. Welded plate is used where a fully continuous shell is required.

A standard galvanized coating is suitable for contact with drinking water, provided the requirements for materials in contact with drinking water are met and the tank is flushed before use.

With zinc-rich paint or zinc metal spray, which restores cathodic protection similar to galvanizing at the damaged spot.

From the pressure needed at the points of use, network pressure losses and the local topography, bearing in mind that about every 10 m of height equals one bar of pressure.