Meta Description: Step-by-step to pick the right corrugated steel water reservoir: calculate capacity, read size charts, choose HDG vs Galvalume vs painted coating, and pick the liner.

We've supplied steel coil to reservoir fabricators for years, and the questions we get haven't changed much. Most buyers walk in knowing the approximate volume they need, but they trip up on two things: they size the reservoir from average daily use instead of worst-case demand, and they pick the coating by price rather than by where the reservoir will actually sit. This guide walks through both.

The formula is simple enough: required capacity equals your daily water demand multiplied by reserve days, plus a fire-fighting reserve. The hard part is being honest about the inputs.

For a farm running livestock and a small irrigation line, we typically see around 40 m³ of daily demand. At five reserve days, that's 200 m³, and unless the local code requires a fire reserve, a 200 m³ reservoir is the right call. For a factory the numbers look different: 600 m³ of process water per day at 1.5 days of reserve gives 900 m³, and most industrial sites need another 100 m³ held back for fire duty - which brings you to 1,000 m³. The fire outlet should be dedicated. Don't let process water draw from the fire reserve.

Corrugated reservoirs are modular, so diameter and height do the work. The table below gives you a starting point; exact volumes come off the inner shell diameter and effective wall height.

One thing we'd flag: above a 20 m diameter, the cost per cubic meter climbs fast. You're paying for wider foundations, heavier bottom rings, and more structural steel. If you can stack two smaller reservoirs instead of one large one, that's often the cheaper route.

This is the section we spend the most time on with customers, because the shell coating is what decides whether your reservoir lasts 15 years or starts weeping at year six.

 Hot-dip galvanized (HDG). It's the baseline. We ship Z275 (275 g/m² total both sides) as standard for inland, fresh-water applications. It's the right choice for farms, municipal non-potable storage, and industrial sites away from the coast. Expect 15–20 years of service with a proper liner, and it's the cheapest per square meter - which is exactly why it's still the default.

 Galvalume (55% Al-Zn). This is the step up. The aluminum forms a stable oxide barrier, and the zinc still provides cathodic protection at cut edges. In humid inland sites or around chemical plants, we see 2–6 times the atmospheric life of HDG. We supply Galvalume steel coil in AZ150 to AZ200 weights for reservoir shells. If your liner gets replaced or inspected over the reservoir's life, Galvalume is the safer bet - the shell doesn't depend entirely on the liner for corrosion protection.

 PVDF, HDP, and SMP color-coated. These systems add an organic top coat over a galvanized or Galvalume substrate. PVDF holds color and gloss for 15–20 years outdoors; HDP sits in the middle; SMP is the budget option. We specify them for coastal installations, mining sites, and any reservoir within about 5 km of the shoreline. Our pre-painted coil line runs PVDF and HDP finishes for reservoir exteriors.

On gauge: don't spec a uniform wall. Hydrostatic pressure rises with depth, so the bottom ring runs 3.5–4.0 mm and the top ring drops to 2.0 mm. A uniform gauge across the wall is a structural mistake we see on fabricated reservoirs every quarter.

The steel shell holds shape; it doesn't hold water. That's the liner's job.

EPDM at 1.0–1.5 mm is what we recommend for potable water. It's NSF/ANSI 61 rated, UV-resistant, and runs 20+ years. PVC is cheaper at 0.5–0.8 mm, but it's for non-potable or temporary use - it degrades in UV exposure. TPO sits between them: flexible, heat-weldable, and a good fit for retrofits on irregular reservoir shapes. Whatever you choose for drinking water, ask for the NSF certificate at delivery.

This is where projects fail on paper. A flat, level base is non-negotiable.

For reservoirs under 6 m diameter and non-potable duty, a compacted sand-and-gravel bed at 95% Proctor density with a geotextile cap works. For anything 10 m and above - and for any potable water reservoir - you want a concrete ring beam. It resists the lateral push of the water column and keeps settlement uniform. Check soil bearing (100 kPa minimum), drain surface water away from the base, and anchor the bottom ring if you're in a seismic zone.

We've lost count of how many times a customer comes to us after the fact. The pattern is always the same: they sized to average flow instead of drought flow, they spec'd HDG for a coastal site, they skipped the liner entirely, or they poured a thin pad instead of a ring beam. A 1,000 m³ reservoir weighs about 1,000 tonnes when full - that's not a load you want improvising on a foundation.

If you have a dimension and a water quality in mind, send them over. We'll come back with a calculated capacity, a coating recommendation for your environment, and an engineered drawing with a quote within 24 hours. Start the inquiry →