Water Storage Tanks UK: A Complete Guide to Choosing the Right Tank
Whether you need to store drinking water, collect rainwater, support an agricultural operation or provide water for a commercial or industrial site, choosing the right water storage tank starts with understanding exactly what the water will be used for.
There is no single tank that is right for every project. Capacity, installation location, available space, water quality and intended use can all affect the type of tank required.
OakPlas manufactures and supplies water storage solutions for domestic, commercial, agricultural and industrial applications across the UK, including above ground water storage tanks, underground water tanks, potable water tanks, slimline tanks and rainwater harvesting tanks.
This guide explains the main types of water storage tank, what they are used for and the factors to consider when specifying a system.
What is a water storage tank?
A water storage tank is a container designed to safely hold water until it is required.
Depending on its specification, a tank may be used for potable or non-potable water storage and can support applications ranging from garden irrigation and rainwater harvesting to agriculture, commercial premises and larger industrial projects.
Water storage tanks can also vary significantly in capacity and shape. The OakPlas range, for example, includes compact slimline tanks beginning at 200 litres alongside substantially larger-capacity storage options.
The right solution therefore depends less on finding the “best” water tank and more on identifying the tank that best matches the individual project.
What is the difference between potable and non-potable water storage?
One of the first distinctions to understand is whether the water needs to be potable.
Potable water is water intended to be safe for drinking. Tanks intended for potable water storage therefore need to be appropriately specified for this purpose.
Non-potable water is water that is not intended for drinking. Depending on the system and application, this can include stored rainwater used for purposes such as irrigation, toilet flushing and washdown.
This distinction matters when selecting a tank. A product should not be assumed to be suitable for drinking water simply because it can physically hold water.
If potable water storage is required, check the specification of the individual tank and any standards or project requirements that apply.
Above ground vs underground water storage tanks
Another major decision is whether the tank should be installed above ground or underground.
Above ground water tanks
Above ground water storage tanks provide accessible water storage without requiring the tank itself to be buried.
They can be particularly useful where there is suitable external space and straightforward access is important.
Applications can include:
- Rainwater harvesting
- Garden and landscape irrigation
- Agricultural water storage
- Livestock applications
- Commercial water storage
- Emergency or backup water supplies
- Potable water storage where the tank is appropriately specified
OakPlas supplies above ground tanks across a broad range of capacities, including compact mini and slimline options as well as heavy-duty bulk water storage tanks.
Underground water tanks
An underground water storage tank can be useful where above-ground space is restricted or where keeping the storage system out of sight is important.
Because the tank is installed below ground, however, the product must be specifically designed for underground installation. Site conditions, excavation, access and the manufacturer’s installation requirements all need to be considered when planning the project.
Neither option is automatically better. The right choice depends on the site and how the stored water will be used.
What is a slimline water storage tank?
Not every property has space for a conventional round tank.
A slimline water storage tank provides an alternative where available width or installation space is limited. Its narrower profile can make this style of tank particularly useful alongside walls, garages, fences and other restricted areas.
The OakPlas above-ground range includes slimline water storage tanks in 200, 400 and 500 litre capacities, providing several options for smaller-scale storage requirements.
Slimline tanks can be useful for domestic rainwater collection, garden watering, mobile valeting and other applications where making efficient use of available space is important.
What is a rainwater harvesting tank?
A rainwater harvesting tank stores rainfall collected from a building, typically from roof surfaces, so that the water can be reused rather than immediately entering the drainage system.
A complete rainwater harvesting system involves more than the tank itself. Depending on the application, the system can incorporate filtration, pumps and controls to collect, store and distribute harvested water.
Stored rainwater can be used for suitable non-potable applications such as toilet flushing, irrigation and washdown, reducing reliance on mains water for tasks where drinking-quality water is unnecessary.
OakPlas offers dedicated rainwater harvesting tanks ranging from compact above-ground options through to high-capacity tanks. Its current range includes capacities from 650 litres to 10,000 litres.
How much rainwater can a property collect?
Potential rainwater collection is influenced heavily by two things: the available collection area and local rainfall.
As a simple starting point:
Roof area (m²) × annual rainfall = potential annual rainwater collection
The result can then be considered alongside expected water demand when assessing the appropriate storage capacity.
For example, two buildings with identical roof areas could have different rainwater harvesting potential if they are located in areas with significantly different annual rainfall.
OakPlas provides a Rainwater Calculator specifically to help estimate potential collection from roof area and local rainfall before choosing a system.
What size water storage tank do I need?
There isn’t a universal answer.
The correct water tank capacity depends on factors including:
- How much water you expect to use
- What the stored water will be used for
- Available installation space
- How frequently the tank will be replenished
- Whether the water is potable or non-potable
- Whether the tank will be above or below ground
- Roof area and local rainfall for rainwater harvesting
- Seasonal changes in demand
- Access and site constraints
Buying the largest tank available is not necessarily the best approach.
For a rainwater harvesting system, for example, tank sizing needs to consider both supply and demand. There is little benefit in specifying substantial storage capacity if the collection area cannot provide enough rainfall to use it effectively.
Equally, an undersized tank may overflow regularly during wetter periods while providing insufficient stored water when demand increases.
Water storage tanks for homes
Domestic water storage can cover several different requirements.
A homeowner may want a compact tank for garden watering, a slimline tank where external space is restricted or a more comprehensive rainwater harvesting system capable of supplying suitable non-potable applications around the property.
For smaller spaces, the physical dimensions of a tank can be just as important as its total capacity.
That is why comparing tank shape, dimensions and installation requirements alongside litre capacity is important when planning domestic water storage.
Water storage tanks for agriculture
Agricultural water demand can be significantly different from domestic requirements.
Farms and rural sites may require water for livestock, irrigation, cleaning or general operational use. Larger sites can consequently require substantially greater storage capacities.
Durability also becomes particularly important when a tank is expected to remain outdoors and perform reliably over a long service life.
OakPlas supplies water storage and rainwater harvesting products suitable for agricultural applications alongside solutions for domestic and commercial projects.
Commercial and industrial water storage
Commercial water storage tanks can support everything from smaller businesses to larger industrial and infrastructure projects.
The appropriate system depends on the site’s water demand, available footprint and intended application.
For businesses looking to reduce reliance on mains water for suitable non-potable uses, commercial rainwater harvesting can also provide a way of capturing rainfall from larger roof areas.
Warehouses, industrial units and other commercial buildings can have substantial roof surfaces, potentially creating significant rainwater collection opportunities.
Why tank material matters
A water storage tank needs to withstand both the liquid it contains and the environment in which it is installed.
Many OakPlas tanks use polyethylene or HDPE construction, with individual products offering features such as UV stabilisation and one-piece moulded construction. Product specifications should always be checked because construction and suitability vary across the range.
For outdoor installations, resistance to weathering and long-term exposure is particularly important.
Where potable water is being stored, the suitability of the specific tank for potable applications must also be confirmed.
Water storage is part of a wider water-management system
For many projects, the tank is only one component of the overall solution.
OakPlas’ wider water and environmental range includes rainwater harvesting systems, septic tanks, sewage treatment plants, grease treatment systems and separators, allowing different aspects of water collection, storage and wastewater management to be considered according to the individual project.
For off-mains properties, for example, wastewater management may involve a septic tank or sewage treatment plant rather than connection to mains sewerage. OakPlas currently offers septic tanks from 2,800 to 11,000 litres and sewage treatment systems for different population requirements.
Commercial sites may instead require specialist grease or washdown separation equipment depending on the wastewater being produced.
Considering these requirements at project level can be more effective than treating every product as an isolated purchase.
Choosing a UK water storage tank supplier
When comparing water storage tank suppliers in the UK, capacity and price are only part of the decision.
Look at whether the supplier can provide clear technical information, explain product suitability and offer a range broad enough to match different project requirements.
OakPlas is a family-run UK manufacturer supporting projects across building and construction, civil engineering, utilities and infrastructure, environmental services, water management, safety and spill control, and merchant and distribution networks.
Its wider product portfolio also extends beyond water management into site and construction products including Rota-Tub® mortar tubs, grit bins, spill management products and material-handling solutions.
That broader manufacturing capability is useful for customers sourcing products across multiple areas of a project rather than looking for a single tank in isolation.
Frequently asked questions about water storage tanks
Can you store drinking water in a water storage tank?
Yes, but the specific tank must be suitable for potable water storage. Do not assume that every water tank is approved or designed for drinking water. Always check the individual product specification and relevant project requirements.
Can a water storage tank be installed outside?
Many water storage tanks are designed for outdoor use, but this depends on the individual product. Features such as UV-stabilised polyethylene can help provide durability for long-term outdoor applications.
Can I bury an above ground water tank?
No. A tank should only be installed underground if it has been specifically designed and specified for below-ground installation. Above-ground and underground tanks are designed for different installation conditions.
What can harvested rainwater be used for?
Depending on the system, harvested rainwater can be used for suitable non-potable applications including toilet flushing, irrigation and washdown.
What size rainwater harvesting tank should I buy?
Tank sizing should consider roof area, local rainfall, expected demand, available space and how the harvested water will be used. OakPlas’ Rainwater Calculator can provide an initial estimate of potential rainwater collection.
Are water storage tanks suitable for commercial and agricultural use?
Yes. Water storage tanks are available for domestic, commercial and agricultural applications. The required capacity, construction and installation type will depend on the individual project.
Find the right water storage solution
Choosing a water storage tank becomes much easier once the application, capacity, location and water-quality requirements are clear.
Whether the project requires a small slimline water tank, potable water storage tank, above ground water tank, underground storage solution or large rainwater harvesting tank, starting with those requirements helps narrow down the options.
OakPlas manufactures and supplies water storage and environmental solutions for projects across the UK, backed by practical product knowledge and a growing range of UK-manufactured products.
If you’re unsure which tank or system is suitable, speak to the OakPlas team about your project requirements before specifying a solution.