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Water Storage Tank Inspection and Maintenance 101

Riley Kooh   |   August 17, 2022

Water is the single most important resource for supporting communities around the globe. Whether it’s for residential, industrial, municipal, or commercial use, water is used in countless ways, many of which we rarely actually see. The United States alone uses 327 billion gallons of surface water every day. But where does this water come from?

An enormous amount of usable surface water is kept in water storage tanks. In North America, the market for water storage systems is estimated at $US 3.4 billion and expected to grow to $US 4.1 billion by 2024. Inspecting these tanks is imperative for structurally sound, clean and safe water for power, agriculture, mining, and household use. Without routine inspections, issues can arise quickly and sediment can build, compromising the integrity and cleanliness of the water.

Types of Water Storage Tanks

Depending on the situation, budget, or environment, there are a variety of water storage tank options to choose from. Each type comes with its own pros and cons, and are better suited for different purposes. Here are the eight most common types on the modern day market.

Fiberglass

Fiberglass tanks are becoming increasingly popular in modern settings. Compared to steel and aluminum, fiberglass is not subject to corrosion or rust. Weighing much less than concrete, fiberglass boasts a respectable strength-to-weight ratio. This makes it an excellent cost-effective option for both installation and long term water tank maintenance. Fiberglass tanks are commonly used for a variety of commercial settings, and can easily be coated for potable water storage.

Fiberglass tanks can be installed both above ground and underground. Underground installation allows for a large amount of water storage, without affecting the usability of the ground topside. These tanks can be completely covered, using a manhole style access point for inspections.

Pillow Tanks

Just as the name suggests, pillow tanks resemble that of a standard pillow. These tanks can be constructed of a variety of materials to store potable water, wastewater, stormwater, gray water, etc.. Their flexible design allows the tank to collapse down for simple transport, with smaller models capable of fitting into a backpack. Commonly used for farms, tree nurseries, firefighting, and military bases, pillow tanks can range from 25 gallons up to an impressive 210,000 gallons.

Concrete

Concrete is the heaviest of material options for storage tanks, however, it is also one of the most versatile. Concrete is in large supply all around the globe, making it an affordable and readily available option for most builds. Additionally, since concrete is a poor conductor of heat, it helps regulate water temperatures in hot climates.

Concrete tanks can be molded to countless shapes depending on the project, and typically last up to 50 years with proper maintenance. However, once degradation sets in, concrete is prone to cracking and has a relatively complex repair process. These tanks are popular permanent storage systems for potable water, rainwater, stormwater, or sewage.

Stainless Steel

Stainless steel water tanks are popular for their safety and durability in both commercial and residential storage. Stainless steel can handle a wide range of temperatures, doesn’t rust, and will not degrade in UV light. Typically used for small-mid size projects due to pricing, stainless steel tanks are commonly used for potable water and beverage production.

Bolted Steel

As the largest storage tank options, bolted steel tanks can be built to hold millions of gallons of water. Although steel can be subject to corrosion, there are treatment options available to avoid this and extend lifespan up to 40 years. These massive tanks are capable of safely storing potable water, and are best suited for large-scale permanent storage solutions. These projects can include the storage of city drinking water, fire protection, wastewater storage, or crude oil storage.

Corrugated/Galvanized Steel

Steel tanks were some of the first renditions of modern water storage. Costing considerably less than its stainless counterpart, galvanized steel is a viable option for lower budget or short-term projects. Since steel corrodes and rusts, it’s integral to have an interior poly lining to protect the material. Even with this poly lining, steel tanks can expect a lifespan of 10 - 20 years. Following a dedicated and cautious inspection process helps maintain the integrity of the lining. Any direct water exposure to the steel tank will induce corrosion and rust.

Polyethylene

Plastic tanks are renowned for their affordability and durability. Polyethylene tanks are built without any interior coating or seams, making for easier water tank maintenance over the long term. They are also completely resilient to corrosion or rust. While steel or concrete tank options can be built to much larger specifications, plastic tanks generally max out at 50,000 gallons. However, for larger projects, multiple poly tanks can be coupled together.

Types of Water Storage Towers

water tower

A water storage tower differs from a general tank by its elevation. By raising a water supply in the air, the force of gravity can be used to create hydrostatic pressure to distribute water supply effectively. Typically water towers are constructed of steel, which provide lifespans in excess of 100 years, and are used to send potable water throughout municipalities.

Standpipe

Standpipe water towers are generally the simplest design for elevated water storage at lower capacities. These ground supported structures resemble, as the name suggests, a standing pipe. This simple design lends itself to a lower upfront cost and a small footprint option for storing large amounts of water. A standpipe design does come with its setbacks though. Due to the high surface area to volume ratio, water temperatures are dramatically affected by weather conditions, resulting in issues with water quality, or thermal stratification.

Read more about real-world Standpipe Cleaning with Deep Trekker ROVs

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Composite Elevated

Composite water towers are a popular choice for large storage projects over 500,000 gallons due to their efficient, stable, and aesthetically suited design for North American cities. Their design is based on a steel tank which is supported by a slimmer concrete pedestal which contains an internal storage and ladder system. The combination of concrete for a foundation structure and steel for water retention is ideal for keeping long-term maintenance costs down, however it can be costly and time consuming during initial construction.

Sphere/Spheroid

Spheroid water tanks are ideally suited for mid size storage between 200,000 and 500,000 gallons. Their design resembles a large sphere supported by either a single or multiple thin legs or pedestales. Similarly to a composite tower, a sphere or spheroid tower benefits from its shape by sheltering much of its water volume from weather conditions, however they generally have no internal storage or ladder system inside the thinner foundation.

Why Clean and Inspect Water Tanks?

Similarly to other assets, being on top of tank inspections will reduce long-term costs by properly prioritizing repair and replacement schedules. If left unattended, many common tank materials are subject to corrosion, cracking, or rusting. The American Water Works Association (AWWA) recommends that potable water towers be inspected every 3 to 5 years. Additionally, many tank manufacturers offer warranties on the condition that tanks are inspected regularly.

Beyond the tank itself, potable water tank inspections are crucial for good water maintenance. Over time, sediment can gather and collect along the bottom of tanks. If in small amounts, sediment has no impact on the quality of the water or on the structural integrity of the storage tank.

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However, over time as that sediment builds up and mixes into thicker ‘sludge’ material, issues begin to arise. These negative effects can result in health concerns for potable water, or tank material degradation from the concentrated substances. Tank manufacturers generally recommend a minimum of one inspection and subsequent cleaning per annum. This is to ensure long-term integrity, extend the tank life, and avoid costly repairs.

How Do I Perform a Tank Inspection?

Traditionally, to inspect a water storage tank without a complete drainage, trained divers would be required. These divers would usually have to be externally hired out, resulting in high hourly costs and coordination complications. If any imperfections are identified, the tank will have to be completely emptied to remove sediment, clean, disinfect, or conduct repairs. After proper time has been allowed for disinfection, the tank can be refilled and measured for contaminants. This process can be costly and time consuming, with considerable downtime depending on the size of the tank.

How ROVs can Improve Tank Inspections

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Minimize Time Required

The use of an ROV for tank inspection and cleaning significantly decreases the time needed to complete the work of maintaining water storage tanks. With quick deployment time, a vehicle can be set up in minutes to get eyes underwater immediately. Without the need to schedule and coordinate with divers, work can be done quickly and efficiently.

Dan Hulands of The Tank Inspectors shared that with the ROV “there’s a lot less set up time, divers require a lot of set up.” Dan also went on to observe that, “the divers know about diving - they don’t necessarily know about tanks. All of our operators know about tanks and have been working with tanks for many years.” With the ROV, tank experts can get their eyes underwater to conduct specialized inspections and cleaning.

Furthermore, the portability of battery powered crawlers and ROVs allow for vehicles to be conveniently transported to a variety of locations within the same day - without the hassle of an external power source. Jeff Conway from the City of Independence noted, “Having a battery powered camera lets us take these vehicles wherever we need without the need of a generator for power”. These lightweight designs also ensure that an operator can safely and comfortably hoist the ROV to the top of taller water tanks.

Maximize Job Effectiveness

By eliminating the need for divers, the use of submersible robotics allows teams to reduce their tank cleaning and inspection costs. Dive teams do not need to be hired every time a tank needs to be looked at, drastically reducing costs over the long-term. Additionally, the deployment and operation of an ROV or crawler only requires one to two employees. Since ROVs can be operated by internal staff, inspections become much more efficient. The pilots know exactly what to be evaluating and can quickly complete a thorough inspection.

Perhaps the most important benefit, tanks can be kept in service and do not need to be drained in order to conduct an inspection/cleaning. Robert Perrin of Ron Perrin Water Technologies shared the convenience of using the Deep Trekker DT640 for standpipe cleaning.

“We use the vehicle instead of divers for tank cleaning,” he said. “Before we got the vehicle we would have to drain the tanks and the utility would lose up to 100,000 of gallons of water.” Michael McAloon, PE, Water/Wastewater Department Manager with Suburban Consulting Engineers echoed this statement, “The Deep Trekker is critical in providing inspection and condition assessment of water storage tank interiors, while maintaining normal system operations.”

Increase Employee Safety

The use of a vehicle eliminates the safety risks associated with divers. The use of submersible robotics ensures that human beings aren’t required to enter any confined spaces or potentially risky situations. The battery powered vehicle also limits contamination risk.

Since generators or other external power sources aren’t being used, Deep Trekker’s ROVs are convenient and reduce the risk of spilling fuel or contamination. Finally, ROVs and crawlers are light and portable, with models as light as 19lbs. This makes them safe for solo staff to transport and handle.

Detailed Documentation

Camera equipped vehicles allow teams to provide detailed inspection videos, photos and reports on their work. Teams can provide clients with professional and thorough documentation of their work. “The ROV is critical in assisting SCE with gathering the necessary information to identify tank deficiencies and problem areas. This information gathered is crucial in our report recommendation for appropriate rehabilitation measures, following tank inspection,” shared McAloon.

Ease of Sanitation

When inspecting water tanks, towers and other water storage facilities it is important to maintain water cleanliness. One of the primary advantages of using an ROV for inspection purposes is that they don’t introduce contaminants to the water the way a diver might. Prior to entering the tank, Deep Trekker vehicles can be fully sanitized with a chlorine solution with no negative effects on the ROV. Keep water clean and free from contamination.

Water Tank Inspection Checklist

Inspect Equipment and Prepare Pump

To start, users should first open their Pelican case and ensure that they have everything they need for the job. It is important that vehicles are given a quick once over to confirm that all required parts are intact and ready for use.

Next the topside pump for the DT640 VAC should be connected and prepared.

Clean Vehicle

Prior to putting the vehicle into the water it should be thoroughly cleaned to ensure safety and cleanliness for potable water sources. Both vehicles and tethers can be cleaned with a hypochloride solution. This procedure is outlined in our Step by Step Guide to Cleaning ROVs for Potable Water Services.

The benefit of using a vehicle for tank inspection and cleaning is the ease in which the robot can be cleaned. One of the major risks associated with sending divers into tanks is the opportunities for contamination from their equipment. There are a lot of “nooks and crannies” on a dive suit that can hold bacteria and other potentially harmful materials to the potable water.

“It’s nice to save my divers from unneeded climbing or entry into a tank that was in good shape,” Mountain West Commercial Diving’s Jake Spaulding adds, “It is so much nicer to hoist the ROV to the top of a tower than it is to send a diver dressed in up a 65 ft ladder. Now we only send in divers if we know what is needed.”

Start Pump and Clear Out Sediment

Once the vehicle has been cleaned and connected to the pump cleaning can begin. Using the lifting hook and rope, the vehicle can be safely lowered into the tank and the pump can be turned on.

Using the handheld controller, operators can drive the vehicle on the tank floor to effectively and efficiently clean sludge.

Inspect

Once the tank has been thoroughly cleaned, it can be inspected to ensure structural integrity. The use of remotely operated vehicles such as the DTG3 is a safe and convenient method for conducting accurate and complete inspections.

The ROV can be driven around the tank to get a close up view of tank walls and floors and roof. Furthermore, video and images can be captured to document any potential issues.

The HD camera and straightforward navigation allows users to get a complete picture of their tank. ROV tank inspection provides users with a convenient and safe way to ensure tank integrity.

Our team is here for any questions you may have, reach out today! Get a customized quote to design the perfect vehicle for you and start improving your inspections today.

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