For drinking water, choose a GRP or stainless steel sectional tank; in our catalogue comparison, stainless steel scores highest for water quality ("Very good") and GRP one step below ("Good"). Galvanized steel tanks are strong and economical, but the TSEK quality certificate shown in our catalogue classes them as not intended for drinking or domestic-use water, so they are best used for fire reserves and other non-potable water. For rooftops, outdoor sites and cold climates, opaque, optionally insulated GRP stands out.
Contents
- GRP, stainless steel and galvanized sectional tanks in brief
- GRP vs stainless steel vs galvanized: comparison table
- What is the best material for a drinking water tank?
- Is a galvanized water tank safe for drinking water?
- How GRP compares with other tank types (catalogue p. 7)
- Rooftop, outdoor and cold-climate tanks
- Which tank for which project?
- Frequently Asked Questions
GRP, stainless steel and galvanized sectional tanks in brief
All three are sectional tanks: standard panels are bolted together on site, so the tank can pass through narrow doorways and be built to the required size (catalogue p. 4). The difference is the panel material:
- GRP: glass-reinforced plastic (chopped glass fibre in unsaturated polyester), hot-pressed in moulds heated to 150 °C (p. 5). See What is a GRP water tank?
- Stainless steel: AISI 304 / 316 L sheet, cold-pressed into panels (pp. 4, 14).
- Galvanized steel: ST 37 hot-dip galvanized sheet, cold-pressed into panels of the same 1,080 × 1,080 mm size as stainless (pp. 4, 14).
For how sectional tanks work in general, see What is a sectional water tank? This guide focuses on the choice of material.
GRP vs stainless steel vs galvanized: comparison table
The three materials differ in panel size, height range, hygiene and outdoor performance; the table sets out the figures from our catalogue.
| Feature | GRP | Stainless steel | Galvanized steel |
|---|---|---|---|
| Material | Glass-reinforced composite | AISI 304 / 316 L | ST 37 hot-dip galvanized |
| Panel size | 1,000 × 1,000 mm (half panel 1,000 × 500 mm) | 1,080 × 1,080 mm | 1,080 × 1,080 mm |
| Tank height | 1.0–5.0 m in 0.5 m steps | 540–4,320 mm in 540 mm steps | 540–4,320 mm in 540 mm steps |
| Standard capacity | No range given in the catalogue; sized per project | 1.26–90 m³; intermediate sizes per project | 1.26–90 m³; intermediate sizes per project |
| Hygiene | Opaque; no algae or bacteria inside (p. 6) | Highest hygiene; no algae or bacteria (pp. 4, 14) | Not for drinking water |
| Outdoors | UV-resistant; optional insulation | Corrosion-resistant | Relies on its zinc coating |
| Density | 1.8 kg/dm³ | Steel, about 4× GRP | Steel, about 4× GRP |
| Assembly | Bolted, no welding; L and U shapes | Bolted on site | Bolted on site |
| Maintenance | Full drain-down via domed floor | Panels replaceable one by one | Panels replaceable one by one |
| Key feature (p. 4) | Opaque, algae-free, outdoor use | Highest hygiene, corrosion resistance | High strength, economical |
| Typical use | Drinking water, rooftops, fire water | Drinking water, hygiene-critical sites | Fire water, irrigation, non-potable process water |
| Catalogue certificate note (p. 21) | Food-contact suitability documented by laboratory reports (catalogue statement) | Listed in the TSEK copy as intended for drinking and domestic-use water | Listed in the TSEK copy as not intended for drinking or domestic-use water |
Panel weight also depends on thickness, and in a full tank the water is the main load (1 m³ of water weighs about 1 tonne).
The certificate notes come from the certificate copies and statements in our catalogue (p. 21). For our certificates, see the Certificates page.
What is the best material for a drinking water tank?
For potable water, the best materials are stainless steel and GRP; our catalogue rates stainless "Very good" and GRP panel tanks "Good" for water quality (p. 7).
- Stainless steel: the highest hygiene in our range; no algae or bacteria form inside (pp. 4, 14).
- GRP: opaque panels stop algae growth. Tests found no heavy metals or phenol and a pH of 6.9 at 20 °C (p. 8). The catalogue states that the food-contact suitability of the GRP panels is documented by laboratory reports (pp. 6, 21).
Material is only half the story: a sealed, opaque roof, a vent (p. 10), a floor that drains fully (pp. 9, 11) and regular cleaning and disinfection (p. 18) matter just as much. For drainage, cleaning and the other features to look for, see drinking water storage tanks.
Is a galvanized water tank safe for drinking water?
We do not recommend galvanized tanks for drinking or domestic-use water: the TSEK certificate in our catalogue classes them as "not intended for drinking or domestic-use water", while it covers stainless tanks for both uses (p. 21).
Galvanized is still a solid tank. The catalogue highlights its high strength and economy (p. 4), and cold-pressed steel panels carry no risk of bulging or bursting (p. 14). Use it where nobody drinks the water: fire water reserves, irrigation water and non-potable process or site water.
Corrosion protection comes from the zinc coating. The zinc is slowly consumed over time, and where it is used up or badly damaged the steel is left open to corrosion, so inspect the tank regularly; a damaged panel can be replaced on its own (p. 14).
How GRP compares with other tank types (catalogue p. 7)
Page 7 of our catalogue rates GRP panel tanks against four other tank types on eight criteria, from Poor to Very good.
| Tank type | Water quality | Watertightness | Durability | Transport | Maintenance | Corrosion resistance | Installation | Recycling |
|---|---|---|---|---|---|---|---|---|
| Aquasan GRP panel tank | Good | Very good | Good | Fair | Very good | Very good | Very good | Poor |
| Concrete tank | Poor | Fair | Fair | Poor | Poor | Fair | Fair | Poor |
| Steel tank | Poor | Very good | Poor | Very good | Very good | Poor | Very good | Poor |
| Stainless steel tank | Very good | Very good | Very good | Very good | Very good | Very good | Very good | Very good |
| Hand-laid GRP tank | Good | Very good | Good | Fair | Very good | Very good | Very good | Poor |
Stainless steel rates "Very good" across the board. GRP panel tanks score "Very good" on watertightness, maintenance, corrosion resistance and installation, but "Poor" on recycling. The "steel tank" row does not specify a coating.
Rooftop, outdoor and cold-climate tanks
GRP stands out for rooftops, open sites and harsh climates: the panels are UV-resistant, opaque and safe to use outdoors in very hot or very cold climates (pp. 5, 6).
- Wind and snow: designed for 60 m/s winds when empty and a 200 kgf/m² snow load on the roof (p. 12).
- Insulation: optional 25 mm CFC- and HCFC-free polyurethane foam prevents condensation on the outside (pp. 5, 12).
- Heat transfer: thermal conductivity is 37.0 for steel, 0.15 for uninsulated GRP and 0.02 kcal/m·h·°C for insulated GRP (p. 12).
On a roof, the water is the main load rather than the panels, so every rooftop tank needs a structural check. GRP also has a temperature limit: in normal use the water stays below 30 °C, with a maximum of 50 °C; tanks for thermal spring water are made to order (p. 12).
Which tank for which project?
The right material depends on what the water is for, where the tank stands and the local climate.
| Project | Material | Why |
|---|---|---|
| Apartment block, drinking water | GRP or stainless steel | Both suit potable water; panels fit through narrow doors (p. 4). |
| Hospital | Stainless first, GRP also suitable | Stainless offers the highest hygiene; drinking and fire water can share a partitioned GRP tank (p. 13). |
| Fire water | Galvanized, GRP or stainless | Galvanized is economical for a fire-only reserve; if the tank also holds drinking water, choose a partitioned GRP tank. |
| Outdoor or rooftop | GRP | UV resistance, wind and snow design loads (p. 12). |
| Process water | Depends on the water | Stainless for hygiene-critical use; galvanized or GRP for cold, non-potable water. Standard GRP is limited to 50 °C (p. 12). |
| Cold climate | Insulated GRP | 25 mm polyurethane insulation (p. 12). |
A partitioned tank also saves space: two separate 2 × 1.5 × 2 m tanks hold 12 tonnes, while a 2 × 4 × 2 m partitioned tank in the same area holds 16, because separate tanks need a 1 m maintenance gap (p. 13). Fire tanks can be planned together with the fire booster sets we build under the same roof (pp. 17, 22).
Size your tank with our capacity guide and tank sizes, check the price factors, then send the capacity, purpose, location and access width through our quote form (p. 23).
Frequently Asked Questions
Is GRP or stainless steel better for a water tank?
It depends on the project. In our catalogue comparison, stainless steel rates "Very good" on all eight criteria, which makes it a strong choice where hygiene comes first (p. 7). GRP is UV-resistant, opaque and available with 25 mm polyurethane insulation, so it is well suited to rooftops, outdoor sites and cold climates; uninsulated GRP conducts heat far less than the steel value in our catalogue (p. 12).
Galvanized vs GRP: which should I choose?
For drinking water, choose GRP: the TSEK certificate copy in our catalogue classes galvanized tanks as not intended for drinking or domestic-use water (p. 21). For fire reserves and other non-potable uses both work; galvanized is strong and economical, while GRP does not corrode and suits outdoor sites.
Should I choose AISI 304 or 316 L stainless steel?
Our catalogue offers stainless steel tanks in both AISI 304 and AISI 316 L (pp. 4, 14). The right grade depends on the water and the setting. Where chlorides are present, for example near the sea or in water with a high chloride content, 316 L is generally preferred for its better corrosion resistance. Send us your project details through the quote form and we will help you choose the grade.
Which water tank material lasts longest?
We do not publish a service-life figure. GRP does not corrode and keeps its shape for many years (p. 6), stainless steel resists corrosion, and galvanized steel depends on its zinc coating. Our tanks carry a 2-year product warranty, with spare parts kept in stock (pp. 3, 18).
Get a quote for your project
Share the required capacity (m³), application and location; our engineers will reply with a recommended panel type, size and material.