The question is never "is it green?" It's "greener than what?"

Every assessment names the product's real counterfactual. A steel bottle's baseline is not "365 plastic bottles a year" unless you actually bought 365 plastic bottles a year — for most people it's tap water in a cup they already own, and against that baseline the bottle never wins.

The most sustainable product is almost always the one you already have. A new purchase is an environmental cost paid up front; only sustained, real displacement of a worse habit redeems it.

Durable "eco" products carry a larger manufacturing footprint than the disposables they replace — a steel bottle embodies the carbon of dozens of PET bottles before its first refill. We state how long each product takes to pay that debt back, under what assumptions, and how realistic those assumptions are: easy, realistic, demanding, or never.

Behavior is part of the math. Surveys show people own four to seven reusable bottles and half replace them within a year — a bottle abandoned before break-even is worse than the habit it was meant to fix.

Manufacturing is often the smallest chapter. Heating wash water can rival a bottle's production footprint; washing and drying are a quarter to a third of a t-shirt's lifetime emissions; electricity is ~90% of an LED lamp's. Each assessment shows the use phase's share of the total and what drives it.

This includes cleanliness — the part eco-marketing never mentions. Reusable bottles grow biofilm without daily washing; bamboo handles mold if they stay wet. Honest hygiene costs energy, and we count it rather than pretend the trade-off away.