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Water Storage Tank Cleaning 101: A Guide to the Process

Riley Kooh   |   June 16, 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 General 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.

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.

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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.

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

DESCRIPTION HERE 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.

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, although most tank cleaning specialists will recommend getting your tank professionally cleaned and serviced at least once a year. 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.

What Causes Water Tank Contamination?

Sediment Buildup

Small levels of mineral sediment in water tanks are common and can be safe, however if left untreated, ‘sludge’ buildup can result in issues. If allowed to settle inside a tank for extended periods, sludge can wear away interior linings and induce corrosion or rusting on steel tanks. Additionally, sedimentation can attract pathogenic micro-organisms which can compromise water safety.

Still Water

Stagnant or motionless water can result in the production of biofilm, which is an ideal host for insects, and crustaceans, or dangerous waterborne pathogens. To combat this, water tanks should implement a mixing system. These systems work to circulate different layers of the stored water to avoid stratification of surface and bottom water.

Vandalization

Whether by humans, animals, or acts of nature, physical damage can pose significant risk to water security. Damaged vents or screens can allow for the entrance of aquatic organisms into the water system.

Why is it Important to Clean Water Storage Tanks?

dt640 utility crawler vacuum cleaner According to the CDC, water borne pathogens put over 100,000 U.S. residents in the hospital every year, and directly cause over $3 billion in direct healthcare costs. These illnesses are not limited to drinking water either. E. Coli outbreaks are regularly linked to contaminated irrigation water, and illness is possible whenever someone swallows, has contact with, or breathes in mists from contaminated water during any household or industrial use.

If a community’s major supply of water comes from a water storage tank, it becomes absolutely integral that the structure is in reliable condition. Any sanitary issues can result in widespread infection risk or water shortages due to tank downtime.

What is the Cleaning Process for Water Storage Tanks ?

Due to the variety of water storage tank designs and styles, there may not be just one standard for cleaning routines. In Ontario, Canada, municipalities and organizations are bound to the Safe Drinking Water Act, 2002, which lays out a standard of care.

At any reasonable time, an officer can conduct an inspection to ensure that stored water is abiding by safety standards. As a general rule, it is recommended that water tanks should be inspected and cleaned at a minimum of once every six months for drinking water and once a year for non-potable water.

 Workers Water Silo

Option 1: Drain the Tank

The most traditional approach to cleaning a water storage tank is to completely drain and have certified workers enter and manually clean the tank. Whenever a human enters a water tank, contamination is a concern. To combat this, proper sanitary PPE must be worn, and all tools must be disinfected. The entire process can be summarized in five steps.

  1. Empty The Tank for Entry To allow for workers to enter and begin cleaning the tank, it must first be completely emptied of its water contents. Ensure that the water is drained into the ground away from plants for safe, legal disposal. All workers must be certified for working in enclosed spaces.

  2. Clean & Rinse Once emptied, workers can vacuum out any sediment, scrub the interior with a detergent, and pressure-wash rinse the interior until all traces of detergent are gone.

  3. Disinfect Depending on the size of the tank, a calculated ratio of water and chlorine-bleach should be added and allowed to sit for a minimum of 4 hours to disinfect the tank.

  4. Drain & Refill Once disinfected, workers can drain the tank again of the chlorine-bleach solution and refill with clean water.

  5. Test & Repeat if Necessary To ensure that chemical levels are safe for human use after cleaning, workers should test water samples and repeat the drain and refill process if necessary.

This method can be extremely labor intensive and costly. While conducting a dry inspection and cleanout, the water tank must be completely taken out of service. This means that alternative water supply must be implemented to prevent shortages and can be logistically or economically challenging. This method also puts workers in potential danger working in confined spaces while handling chemicals. Additionally, cross contamination is always a concern whenever humans enter the tank, even if all precautions are taken.

Talk to us about how our ROVs improve the safety, cost and speed of water tank inspections and cleanings

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Option 2: Water Tank Cleaning Divers

As an alternative to dry cleanings, commercial divers can be hired to clean water tank interiors without any dewatering. Typically done in a team of three, one diver will enter the water while two remain topside as ‘spotters’. Before entering, the diver’s wetsuit will be completely disinfected. Once inside, they will use a vacuum system to pump sediment to the surface for removal, and report on the condition of the tank structure.

The most notable benefit of this over dry cleaning is the ability to maintain water in the tank. Dewatering can waste thousands of gallons of water and can sideline water supplies for multiple days. However, some negative considerations of divers are the cost, risk, and time consumption.

Due to the complexity of performing submerged tasks, commercial divers undergo rigorous certification, which reflects in high hourly cost. Additionally, the associated dangers of diving in confined spaces with single exits puts divers at risk and can increase the risk premiums. Divers are also limited to their gas supply, meaning frequent resurfacing which can extend cleaning times. While proper sanitation should always be performed pre-entry, having divers directly enter the water does carry the risk of cross contamination as well.

Option 3: Robotic Tank Cleaning With ROVs

Inspection Robot Implementing a Remote Operated Vehicle (ROV) is another option for tank inspections and cleanings without draining the tank. These vehicles come standard with HD cameras, and can be equipped with multi-intake vacuum heads and pressure washers to complete a tank cleaning fully remotely.

The disinfection process is much simpler for an ROV in comparison to humans, and can be done by simply soaking or spraying the vehicle with a solution. Thanks to extended battery lifes, cleanings can be completed quickly with zero or minimal breaks. Since the operator can remain topside, there is no risk associated with diving or entering confined spaces, and all imperfections can be easily recorded and used for asset monitoring.

The Benefits of Using Deep Trekker ROVs for Water Tank Cleaning

Keep Water Tanks Online

The main benefit of Deep Trekker ROVs in lieu of a dry cleaning is to keep water tanks online. With water conservation becoming a growing concern, throwing away thousands of gallons of usable water is far from the ideal solution.

For an example, we look to Ron Perrin Water Technologies. Previously, they would drain a 110ft standpipe of up to 100,000 gallons of usable water in order to clean the tank interior. After purchasing a DT640 VAC from Deep Trekker, they were able to accomplish this quicker and easier, while wasting zero water.

Reduce the Use of Divers

While there will always be a place for commercial divers for certain projects, ROVs can effectively streamline tank cleanings in lieu of divers, thus lowering costs, improving efficiency, and maximizing safety.

For testimonial, we look to The Tank Inspectors, a 30-year established water tank service and installation company. After purchasing a DT640, Operations Manager Jo Hulands noted that where the team used to have to put a diver in the water, they can now use the ROV. “Pretty much 80% of the tanks that we do we can clean with the vacuum cleaner”.

By using the ROV in lieu of a human diver, The Tank Inspectors not only keep humans safe but save time and money. In addition to OH&S standards regarding people in tanks and limiting the time people can actually be in the tanks, Dan noted that with the ROV “there’s a lot less set up time, divers require a lot of set up.” Furthermore, the divers require scheduling and coordinating where the DT640 can be deployed quickly and conveniently.

In addition, the use of the DT640 saves the Tank Inspector team significant amounts of money, estimating that the ROV is “40% of the cost of using divers.” “In fact,” Jo continued, “many diving companies themselves use the ROV to limit dive time by scoping out jobs with the DTG3 and undertaking cleans with the DT640.”

Check out the full case study here.

Easy To Disinfect

One of the major risks associated with sending divers into tanks is the chance of contamination from their equipment if they do not follow a strict procedure. 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.

Water Inspection WorkersThe DT640 VAC Being Sprayed with Disinfectant

For a Deep Trekker vehicle, disinfection is simple and reliable, thanks to their compact and intuitive design. To disinfect, simply spread the vehicle and tether on a clean and disinfected ground sheet. Then, thoroughly spray down materials with a chlorine-bleach disinfection solution. Alternatively, the vehicle and tether can also be soaked in the solution. Note that all plastic ropes and cables, used to hoist a vehicle for example, must be treated in the same manner.

Portable

Deep Trekker’s vehicles operate using lithium ion batteries instead of direct power from generators. The absence of topside power drastically reduces the overall footprint of the setup, allowing for the vehicles to transport in either one or two Rugged Pelican Cases. At 34lbs base weight, the DT640 VAC can be effectively hoisted to the top of water towers by a single operator. Water Inspection WorkersRon Perrin Water Technologies Hoisting a DT640 VAC up a 110ft Standpipe

The handheld controller and tether system are also designed with portability in mind. Replacing large control consoles and bulky tether is essential for maneuverability. The included tether utilizes a polyurethane outer jacket with embedded synthetic fibers to achieve a 200lbs working strength at under ¼ inch diameter to fit on a compact reel system. The combination of controller, tether, and battery powered vehicle simplifies working at heights and provides superior portability between jobs.

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