No one considers their water tank. Until it gets screwed up, anyway — and then, for a few days it’s the most important thing in the building. These are the things that occur during the hottest part of the summer when you’re least expecting them, and they do happen.
What’s good is that the maintenance of the water tank is not a complicated process. It just needs to be consistent. Everything you need to know to keep your tank in good working order, water clean and to ensure maximum service life.
Routine Water Tank Maintenance Is So Important
One of the most underutilized assets of any home, business or industrial property is a water tank. It’s just expected to hold water and to be able to release it as and when needed. Until it doesn’t.
Sediment accumulates over time, biofilm forms on the inside walls and minor problems slowly become major problems. There’s no such thing as prevention being too cheap after the crisis.
This is a real health aspect as well. Legionella bacteria are responsible for the potentially deadly pneumonia named Legionnaires’ disease, and are found in stagnant, warm water tanks. CDC has named the following factors that can contribute to the growth of Legionella: water age, water temperature, water disinfectant, biofilm, and sediment. All of those are something that can be managed regularly and proactively.
Water Tank Maintenance Life: How Long, Anyway?
It is important to have realistic expectations before we get to the actual maintenance schedule — just as with any tank, the life of the tank is dependent upon the material and, even more, the maintenance schedule that is followed.
The life expectancy of the concrete tanks is 20-30 years, while those tanks which are properly maintained can serve over 50 years. Usually, the service life of polyethylene plastic tanks is 10 to 20 years, but if they are enclosed in a sheltered facility, they may last 25 to 30 years if they are high quality and treated with UV stabilisation. Typically, stainless steel tanks have a service life of 20 years or longer if they are not subjected to severe service conditions, and with proper coating and maintenance, a steel tank can last up to 50 years in a favourable service environment.
As in all cases with tanks, the range between the minimum and maximum possible tank life is mainly due to maintenance. A concrete tank that is now 50 years old accomplished that by routine inspection and maintenance. Failure at age 15 was almost always due to neglect.
1. Conduct Periodic Inspection(s) at Least Once Per Year
Many guidelines, such as HSG274 Part 2 in the UK and ASHRAE Guideline 12-2000 recommend annual inspection and cleaning of hot and cold water systems with elevated storage tanks to reduce the potential for bacterial growth.
A proper inspection is done on the outside and inside. From the outside, look for spots of dampness, stained surfaces, cracks in the surface, and fittings, valves, and pipe connections. Examine the interior of the tank after draining for sediment at the bottom, biofilm on the wall and floor, rust, mould and insect or vermin access.
NEVER omit the lid and access hatch. An ill-fitting cover or damaged cover allows insects, airborne debris and microorganisms to get into the tank — a tank that appears to be completely clean on the outside may be quite contaminated on the inside if the cover has not been properly fitted.
Bacteria samples should be taken at 6 month intervals for drinking water tanks. The frequency of testing should be determined by the risk assessment and control plan for any non-potable applications.
2. Thoroughly Scrub the Inside of the Tank at Least Once a Year
The condition of the tank will be revealed through inspection. Cleaning is the solution which makes it right. Annual cleaning is not always legally mandated in all jurisdictions, but annual inspection is almost always legal and will usually reveal something that requires cleaning anyway.
It doesn’t matter when, but it does matter how. Empty the tank completely before cleaning the tank base and walls. Remove sediment from the bottom using suitable equipment. Use a neutral non-abrasive solution and a stiff brush to clean interior surfaces or a mild high pressure wash that will not damage any interior coating. Wait for some time after applying the cleaner then drain it and air dry the tank before refilling it with water.
After a tank is cleaned, use an appropriate concentration of a chlorine solution to disinfect the tank to ensure the safety of the drinking water, when disinfecting after cleaning the tank is required. Rinse thoroughly with clean water after removing the tank and before putting it back into service to remove excess chlorine.
As always, as you’re entering a confined space, in this case a water tank, do not do it without proper training, risk assessment and equipment. Proper precautions are essential for confined space entries and these preventable accidents occur annually.
3. Control Water Temperature to Reduce Bacterial Growth
This is the simplest maintenance task to forget, and the science behind it is relatively simple. The temperature range at which Legionella bacteria multiply best is from 25°C to 45°C. The CDC suggests hot water be stored at temperatures above 60°C and cold water kept below 20°C, thus extending the storage range on both sides of this temperature growth range.
Uninsulated water tanks placed in roof spaces or in warm climates with a window or roof opening to the sun can be hot enough to promote bacterial growth. Cold water tanks need to be well-insulated to keep the water in them cooler. Hot water systems, on the other hand, require insulation all throughout to maintain water temperature at a steady level that is safe.
Make sure to check temperatures at selected locations, especially at the remote outlets. If hot water isn’t reaching the desired temperature at these far distant locations, it’s likely the system may need a closer inspection for the design or insulation.
4. Test for Leaks, Cracks, and Structural Damage
Uncontrolled leaks create serious health and monetary issues. A small hairline crack on the tank allows water to penetrate its surface and helps to promote mould and structural deterioration – and continually drains water out of the tank. It’s an expense that accumulates on a large tank, or if water is an important cost in a region, the problem can be a continuing one.
While hairline cracks in a concrete tank are not necessarily a problem, if they are leaking or water is entering or exiting the tank, they should be addressed immediately. If the water in the tank has discoloured or cloudy, it may indicate that the inside of the tank is deteriorating or contaminated. Low water pressure can also indicate a leak in the walls or pipework of the tank.
Surface crazing, deformation or brittleness – watch in plastic tanks, particularly those exposed to a lot of UV. Polyethylene will degrade in direct sunlight with time, and will develop cracks and structural failure. If possible, store plastic tanks in shaded areas or provide plastic tanks with UV protection.
Inspect all lines of service (inlet and outlet valves, pipe connections) during all maintenance checks. Before it becomes a leak point, tighten or reseal any loose joints.
5. Manage Sediment Build-Up
As time goes on, sediment is deposited into all water tanks. It is deposited at the base where there is low flow or no flow, and is also a source of nutrients and surface for the growth of bacteria, including Legionella. Opportunistic pathogens have been repeatedly found in higher numbers in water storage tanks where sediment build up has been observed.
Tank are periodically flushed (not only once a year when they are cleaned) which helps to reduce sediment accumulation. Both ASHRAE and OSHA advocate hot water storage tank drainings annually in an effort to remove scale and sediment deposits. Regular flushing is also a way to keep energy costs lower because sediment and scale also lower the heating efficiency, forcing the heating system to work harder.
In industrial and larger commercial tanks, the common sense approach is simple: If sediment is monitored regularly, then action is taken before corrosion or deterioration of water quality occurs locally.
6. Keep Valves, Fittings and Connected Equipment in Good Repair and Running Condition Promptly
A water tank is as dependable as all its components; inlet and outlet valves, float assembly, overflow pipe, and filters on the water system. A leak or broken float valve results in water continually overflowing, and will waste water and lead to damage of the surrounding structure. When the inlet filter is clogged, it cuts off the supply. A pressure limiting outlet valve is used.
Double flush all valves that are connected every two years. Keep overflow pipes clear with water safely directed away from the building. Periodically check filter housings for sediment loading and change the filter media as specified by the filter supplier. In the event the tank contains a thermostatic mixing valve, maintain it twice a year following the manufacturer’s recommendations (one of the most common causes of thermal failure in tanks).
Record all services, tests and corrective actions performed. If there is no record it is not possible to identify a pattern of risk or show compliance if an inspecting authority requests it. In general, store maintenance records for a period of five years.
7. Resist Damage and Contamination from Sun, Air and Environment
It’s very simple to avoid damaging the service when it’s done, and much harder to repair the damage after it occurs, especially if it is done gradually.
Over time, even plastic tanks that are made with a UV inhibitor will deteriorate when exposed to UV rays. It is sensible to prevent tanks from long periods of direct sunlight or to provide comprehensive protection from it. The first external challenge to metal tanks in coastal regions is salt-air corrosion and protective coatings require periodic checks and maintenance to remain intact.
Maintain cleanliness around the tank without any debris. An unorganized or dirty tank room makes inspections more difficult and makes it more likely that contaminants are added to the tank during regular maintenance tasks.
When to Call in a Professional
Some maintenance tasks are really only appropriate for trained and certified personnel, such as cleaning and disinfections, entry into confined spaces, Legionella risk assessment and major structural repairs. It’s not over-cautious by itself: poor water quality has health implications, and cleaning chemicals have hazards if not used properly.
Generally replacement is more cost-effective than repair when the repair cost is about 50% of the replacement cost. The cost of downtime and consequent risk far exceeds the initial expense of more regular pro-active maintenance for an ageing tank.
You Will Be Able to Follow This Simple Water Tank Maintenance Schedule
Regularly monitor water colour, pressure and water quality. Double service valves and fittings twice a year. Monitor temperature twice a year at sentinel locations. Sample for bacteria twice yearly. Have a complete internal/external inspection once a year. Replace drinking water tanks every year and clean and disinfect.
It is not a rigid one-size-fits-all program — it is a realistic program that is consistent with generally accepted industry practice, and when followed diligently will keep most tanks operating within their design-life for the most part.
In fact, the maintenance tips are of little or no use unless they are applied. Schedule reminders, record results and tackle small problems before they are large ones. You will no longer see how much your water tank appreciates it — or how much it will fail you!