Rainwater Collection Tank Size Grades: How to Read Them | Bidragon Steel Silos

Rainwater collection tanks are sold in size grades, and the size table for the tank on this site is the clearest way to compare those grades, provided it is read correctly. The rainwater collection tank on this site is a circular corrugated sectional steel tank, made of galvanized steel plates of different sizes as wall panels with food-grade waterproof cloth as the inner lining in contact with water, and described as suitable for drinking water storage. This article explains how to read its size table, what each column means, and what the table does not say.

The size table has a fixed height for every grade: 3.36 metres. That fixed height is a useful fact, because it means the grades differ in diameter and volume, not in height, and the foundation, the site footprint and the access requirement change with diameter rather than with height. A buyer with a height limit should therefore check it against the fixed 3.36-metre height, and a buyer with a footprint limit should check it against the diameter for the grade, not against the volume alone.

The grades in the table run from 55 cubic metres at a diameter of 4.58 metres, through 108 cubic metres at 6.4 metres, 218 cubic metres at 9.1 metres, 319 cubic metres at 11 metres, 562 cubic metres at 14.6 metres, 1163 cubic metres at 21 metres, 1494 cubic metres at 23.8 metres, to 1994 cubic metres at 27.5 metres. The pattern is straightforward: as the diameter grows, the volume grows faster than the diameter, because volume depends on the square of the diameter at a fixed height. A buyer who needs, for example, twice the volume does not need twice the diameter, and a buyer comparing two grades should compare both the diameter and the volume, not one column alone.

Each grade also carries a monthly production figure, and that column is the most commonly misread column in the table. The figures run from 400 sets per month for the smallest grade down to 66 sets per month for the largest grade, which reflects the fact that larger tanks take more material and more work per set. Those figures are production figures from the product page. They are not stock levels, they are not delivery promises, and they are not lead times. A buyer should not read a monthly production figure as meaning that a given number of tanks is available for immediate delivery, and delivery scope and timing should be confirmed per project through the inquiry form.

The foundation requirement is given as 100 to 150 millimetres, by size grade. That range is a foundation thickness figure from the product page, and the applicable value within the range depends on the grade and the site. A buyer should confirm the foundation requirement for the specific grade proposed, together with the ground preparation, drainage and access requirements, because a tank foundation that is too thin or poorly prepared will affect the tank over its working life. The documented service life for this tank is more than 10 years, and that figure should be read together with the lining, the maintenance regime and the water quality, not as a standalone guarantee.

The size table on this page applies only to the rainwater collection tank. It must not be applied to the galvanized water storage tank on this site, which is a different product with its own product page and no size table. The galvanized tank is described as a very large tank of corrugated galvanized steel plate, with assembly within 1 to 5 days and an expected life of up to 50 years with regular maintenance, but those figures are for that product, not for the rainwater tank, and the two products should not be merged into a single size range.

Choosing a grade starts with the water requirement, not with the table. A buyer should work out the daily or weekly water demand, the rainfall and catchment available, the storage duration needed to bridge dry periods, and any fire, irrigation or domestic requirement that sets a minimum volume. That required volume then points to a grade in the table, and the diameter for that grade can be checked against the site footprint. Where the required volume falls between two grades, the choice between the smaller and the larger grade depends on the cost of running dry against the cost of the larger tank and foundation, and that trade-off should be discussed with the supplier.

In summary, read the rainwater tank size table by grade, check the fixed height against any height limit, check the diameter against the footprint, read the volume as the storage capacity for that grade, and read the monthly production figure as a production figure, not as stock or delivery. Confirm the foundation requirement, the lining, the delivery scope and the price for the specific grade through the inquiry form. The relevant pages on this site are the rainwater collection tank page, the galvanized water storage tank page and the steel water tanks category page.

The inner lining deserves attention when a rainwater tank will store drinking water. The rainwater collection tank on this site uses food-grade waterproof cloth as the inner lining in contact with water, with galvanized steel plates as wall panels. A buyer storing drinking water should confirm the lining material, its food-grade status, how it is joined and sealed, and how it is inspected and replaced over the tank's working life. A buyer storing irrigation or construction water has different requirements, and the lining, the outlet arrangement and the overflow provision should be matched to the intended use rather than assumed from the tank format alone.

Overflow and drainage planning is part of sizing a rainwater tank, not an afterthought. A tank that fills in heavy rain needs a safe overflow route, and a tank that stands on a poorly drained foundation will suffer from waterlogging around its base. A buyer should plan the overflow discharge, the foundation drainage and the access for inspection and cleaning at the same time as choosing the tank grade, and should confirm the foundation requirement for the specific grade proposed. The documented foundation range for this tank is 100 to 150 millimetres by size grade, and the applicable value within that range should be confirmed per project.

Related pages

• Silo Selection Guide
• Silo Cost Guide
• Contact via the inquiry form