Every water storage tank gets a score from 0 to 100% built from four factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Products are grouped by total gallons stored (under 25 gallons, 25 to 49 gallons, and 50 gallons and up) and use the same scale in every group.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per gallon stored | 40% |
| Potable claims | NSF certification, food-grade materials and BPA-free, as published | 25% |
| Features | an included spigot or outlet fitting, stackability and UV resistance | 20% |
| Warranty | the maker's warranty | 15% |
Where the numbers come from
Capacity, dimensions, weight and material claims come from the maker’s product pages or spec tables: RomoTech’s catalog, WaterPrepared’s product pages, Norwesco’s tank tables and RecPro’s product pages. Where a maker has no page for a model, the figures come from the listing the maker’s own store publishes on Amazon, and the product page says which. Prices are Amazon prices for a new item. A figure the maker doesn’t publish is left blank rather than taken from a retailer or estimated. For multi-packs, capacity is the total gallons in the pack and the size and weight are for one container.
The factors
Value is the current price divided by the total gallons stored, on a log scale, so halving the price per gallon always counts the same. $12 per gallon scores zero and $2 per gallon full marks.
Potable claims adds what the maker publishes about water safety: NSF or ANSI/NSF certification (half the score), food-grade or FDA-compliant materials (three tenths) and a BPA-free statement (two tenths). A tank with none of these published scores zero and is marked estimated; that does not mean the tank is unsafe, only that the maker doesn’t say.
Features adds the things that make stored water easier to use: an included spigot (0.35) or, failing that, a built-in outlet fitting (0.2), a maker-stated stackable design (0.3) and UV resistance (0.35).
Warranty is the maker’s warranty on the product: 1 year scores zero and 10 years full marks. A product with no published warranty scores zero and is marked estimated.
What isn’t scored
Size and weight, material, and whether a container stacks when full are listed but not scored. A tank’s footprint is a fit question, not a quality one, and weights are only published for some models. Water quality, leaching and taste aren’t tested here, because no independent measurements have been published for these products.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated. The exceptions are potable claims, features and warranty: a claim the maker doesn’t publish counts as none, so the factor scores low and is marked estimated where a published claim could change it.
What isn’t ranked
Rain barrels sold for garden use with no potable rating, collapsible bladders, bathtub liners, water bottles, filters, steel and fuel tanks, and underground cisterns aren’t ranked. Products with no maker spec and no usable photo are held back until they turn up.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.