The perceived advantage of elevated water tanks on high tank stands that rely on gravity rather than electricity for water delivery, is rapidly becoming an outdated misconception. They’re no longer the first, only, or ultimate solution. In modern times, cutting-edge technology is able to replace the ancient practice of gravity-reliant systems.
Below are some notes on structurally elevated tanks compared with round/circular, ground-level tanks:
Any water supply requires delivery at a minimum workable pressure. An acceptable working pressure for domestic purposes is around 2.5 Bar… roughly speaking. Less than 2 Bar may be troublesome. 3 Bar or more is great!
But 2.5 bar pressure requires a tank stand height of at least 25 m! And herein lies the challenge associated with elevated tanks – how to safely support that tremendous weight… at considerable height?
As an example: since 1000l of water weighs 1 tonne, an elevated tank of say 100,000 litres would require a structural framework capable of supporting at least ONE HUNDRED TONNES … at 25m height in order to provide pressure of 2.5 Bar. Scary!
Some important considerations when opting for elevated tanks:
- Specialized, advanced engineering design
- tonnes of additional structural steel for the tank stand
- this tank stand steel requires protective coating and ongoing maintenance
- lengthy on-site construction costs for what are essentially two different projects:
1. the steel tank construction
2. the steel tank stand construction.
- THE COST OF THE ELEVATED TANK STAND MAY FAR EXCEED THE COSTS OF THE WATER TANK ITSELF!
- even if gravity does replace an output pump, an energized input pump is usually necessary
- safety and risk assessments
- destruction of property (or loss of life!) in the event of failure and collapse of the support structure
- soil substrate stability supporting the weight of the combined tank and tank stand assembly
- high winds to which the square, the elevated tank may be subjected
- longevity of the tank stand’s structural steel components
ROUND, GROUND-LEVEL WATER STORAGE TANKS
A round, ground-level water storage tank is positioned directly onto the ground on suitable substrate, entirely negating construction of a tank stand. This results in a massive saving in costs related to structural steel and construction time.
If a ground-level water tank IS able to be positioned on a suitably high point (such as a hill or kopje), it can also function as an indirect delivery system (gravity feed), requiring no output pump. However, with no naturally elevated landscape feature nearby on which to elevate the ground-level tank, it will require an energized output pump to deliver the required water pressure.
But is this really a ‘negative’?
Considerations for the utilisation of round, ground-level tanks:
- several remarkably inventive solutions exist nowadays for ground-level tank pump systems
- such pumps have the advantage that flow rate can be directly adjusted and controlled.
- costs of a pump system may be substantially less than that of an elevated steel tank stand structure.
- Ground-level tanks are considerably cheaper to install than elevated tanks of the same volume.
- Should stored-water volumes need to be increased, it’s much easier (and cheaper!) to simply install an adjacent ground water tank or to increase the capacity of the existing tank by increasing its wall height. Not so simple for elevated tanks!
- Round vs square tanks. Since round water tanks offer far less wind resistance than square tanks do, round tanks are inherently more stable in adverse weather conditions… less risk!
Elevated tanks and round, ground-level tanks are simply bulk water storage vessels:
- One delivers gravity feed while the other requires an output pump (that is, if the ground-level tank is unable to be elevated on a suitably high geographical feature).
- In both cases, pumps are required for water input purposes.
- Output pump cost in ground tanks is hugely offset by the excessive cost of the tank stand structure required for elevated tanks.
- Complexity and time of construction – ground-level tanks are easy and quick to install.
- Costs – overall, a round, ground-level tank can cost less than half of the price of an elevated tank of the same volume.
Due to the advances nowadays in highly-efficient pump technology coupled with a host of alternative power generation options, ground-level tanks such as those installed by Rainbow Reservoirs, are becoming an increasingly popular choice over elevated tanks, especially in small to medium-scale applications.