12 Types of Water Tanks in Commercial Buildings

Introduction

If you’re managing a commercial property in the UK, chances are you’ve already come across the challenge of understanding which water tanks serve what purpose—and how to keep them in top working order. From keeping heating systems running efficiently to ensuring safe drinking water, water storage tanks are critical to a building’s infrastructure. Knowing the differences between them, when they’re used, and what upkeep they require isn’t just useful—it’s essential.

This guide breaks down the most common types of water tanks you’ll find in commercial buildings and explains how each one fits into broader building operations and compliance standards.

Why Water Tanks Matter in Commercial Facilities

Water tanks aren’t just backup containers—they’re often integral to daily building performance. Whether it’s maintaining steady pressure in plumbing systems, supplying emergency reserves, or separating systems to avoid contamination, tanks underpin many of the unseen but vital processes that keep a building functional.

For facilities managers, understanding these tanks allows for better risk management, improved energy and water efficiency, and smoother communication with contractors, engineers, and compliance bodies.

Types of Water Tanks and What They Do

Potable Water Tanks

Potable tanks store drinking water that’s used for human consumption, handwashing, food prep, and hygiene. In commercial settings like offices, healthcare, or hospitality, these tanks are usually constructed from GRP (Glass Reinforced Plastic) or stainless steel to meet hygiene and water regulations. Keeping these tanks sealed, clean, and protected from microbial growth is vital to ensuring compliance and water safety.

Feed and Expansion (F&E) Tanks

These tanks are part of open-vented heating or hot water systems. They serve two purposes: feeding water into the system and absorbing the thermal expansion that occurs when water heats up. Typically installed at high points, like plant rooms or roof spaces, F&E tanks must be capable of withstanding fluctuating temperatures. Corrosion, scaling, and bacterial build-up are key risks to monitor here.

Header Tanks

Header tanks help maintain pressure in gravity-fed plumbing systems—often in older or multi-storey buildings. They act as a buffer when water demand changes suddenly, helping to avoid issues like airlocks or pump cavitation. Like F&E tanks, these are often tucked away at height and should be regularly checked for insulation, tight sealing, and cleanliness.

Break Tanks

Break tanks introduce an air gap between the mains water supply and a building’s internal system to prevent backflow and contamination. They’re commonly used where mains pressure isn’t reliable or where regulations (like those from WRAS) require physical separation. Proper sizing is key—especially in high-demand buildings—to prevent pressure drops or supply interruptions.

Holding Tanks

Holding tanks store non-potable water for secondary uses such as cooling towers, industrial processes, or irrigation. These tanks give buildings the flexibility to store water during off-peak hours or capture alternative supplies (e.g. borehole or reclaimed water). The material—often polyethylene or steel—should suit the temperature, pressure, and chemical profile of the stored water.

Process Tanks

These are custom-designed tanks used in manufacturing or specialised facilities where water or other fluids need to be stored, mixed, or chemically altered. They're typically part of a larger process system and must be compatible with whatever substances are involved. This is where bespoke design, material compatibility, and ongoing monitoring really come into play.

Sprinkler Tanks

Sprinkler tanks store dedicated water for fire suppression systems and are built to strict regulations such as BS EN 12845. Whether it’s a single gravity-fed tank or a sectional unit feeding a pumped system, it’s vital that these tanks are regularly tested and maintained. System failure due to a neglected tank could be catastrophic—so inspections, flow tests, and alarm checks are non-negotiable.

Cat 5 Tanks

Cat 5 tanks are designed for storing water where there’s a high risk of contamination from harmful substances—commonly used in environments like chemical washdown areas, vehicle cleaning bays, or anywhere fluids could pose a serious health hazard if backflow occurs. These tanks are part of a fluid category 5 system under the Water Supply (Water Fittings) Regulations, meaning they must include specific backflow prevention measures such as air gaps or AB air gap assemblies. In commercial settings, correctly specified Cat 5 tanks are vital for regulatory compliance and public safety, especially where non-wholesome water may come into contact with potable systems.

Soft Water Tanks

Soft water tanks store water that has been treated to remove hardness-causing minerals like calcium and magnesium—either through ion exchange softeners or other methods. These tanks are typically used in buildings where scale build-up needs to be avoided, such as those with steam boilers, humidifiers, or delicate plant equipment. In commercial facilities, softened water helps extend the life of heating systems and appliances, improves energy efficiency, and reduces maintenance costs associated with limescale. It’s important, however, to ensure soft water is only used where appropriate, as it isn’t suitable for all potable or process applications.

Specialist & Sustainable Storage Tanks

Irrigation Tanks

Designed for landscaping and grounds maintenance, irrigation tanks help manage water sustainably. These can be supplied from mains water, boreholes, or captured rainwater, and are often fitted with filtration to protect sprinklers or drip lines. In areas with hosepipe bans or water restrictions, having a reliable irrigation tank is a practical asset.

Rainwater Harvesting Tanks

These tanks collect water from roofs or paved surfaces, filtering and storing it for use in flushing toilets, vehicle washing, or irrigation. For buildings aiming to improve sustainability credentials or gain BREEAM points, rainwater harvesting can be an effective strategy. Tanks may be installed above or below ground, depending on space and volume needs.

Grey Water Tanks

Grey water tanks store reusable wastewater from sinks, baths, and washing machines—excluding toilet waste. Once treated, this water can be reused for flushing or irrigation, helping to reduce reliance on potable supplies. In high-occupancy commercial buildings, these systems can significantly cut water bills, but must be carefully designed and monitored to meet hygiene standards.

Materials Matter: What Tanks Are Made From

Selecting the right material is more than a budget decision—it’s about performance, hygiene, and lifespan. Here’s a quick breakdown:

• GRP (Glass Reinforced Plastic): Modular, corrosion-resistant, and commonly used in indoor plantrooms or rooftops. Panels can be assembled in tight or awkward spaces.

• Plastic (Polyethylene/Polypropylene): Lightweight and suitable for above-ground tanks storing low-risk fluids.

• Fibreglass: Strong, chemical-resistant, and ideal for industrial or aggressive environments.

• Concrete: Durable and secure—often used underground due to its weight and long service life.

• Stainless Steel: Robust and hygienic, ideal for potable systems or high-demand environments.

Each material has a sweet spot in terms of durability, cost, and application—matching the tank to its environment is key.

Maintenance and Compliance

Whether it’s for fire suppression or drinking water, tanks must be regularly inspected and maintained to stay compliant and safe. Key actions include:

• Visual inspections for leaks, corrosion, insulation integrity, and access security.

• Cleaning schedules to remove sediment, algae, or bacteria (particularly for potable or open tanks).

• Water testing to monitor for Legionella or other microbiological hazards.

• Record keeping for audits, insurance, and regulatory bodies.

UK legislation like the Water Supply (Water Fittings) Regulations 1999, WRAS guidance, and building insurance terms all point to proactive tank maintenance as a necessity—not a luxury.

Final Thoughts

Water tanks are easy to overlook—until something goes wrong. For facilities managers, understanding the types, functions, and care requirements of these tanks can reduce risk, improve efficiency, and keep your building compliant with health and safety standards.

If you ever need support with specifying, installing, or maintaining water tanks, partnering with a specialist like Titan Mechanical Services can offer peace of mind and practical solutions tailored to your site.

If you'd like to learn more about water tanks, then visit our Cold Water Tanks page where you will find a library of information.