See how fast a filter pays for itself.

A household that drinks bottled water often spends far more than one using a tap filter. A typical family buying 4-5 bottles a day can spend 50-100 a month on water alone. A filter jug or under-sink system costs 30-300 upfront plus 40-120 a year in replacement cartridges, which is usually cheaper from the first few months.

The break-even point matters more than the long-term total. A 60 filter jug with 80 annual cartridges pays for itself against a 40 monthly bottled habit in around 1.5 months. After that, every month is pure saving. Bigger systems like reverse osmosis cost more upfront but scale to family-size usage better.

This tool keeps it simple: it compares total bottled spend over your chosen years with the filter's upfront plus ongoing cost. It does not account for bottled water health or taste preferences, which are personal, or for waste reduction benefits. The output is a direct cost comparison only.

Run it with sensible defaults

Using bottled water monthly spend of 40, filter system upfront cost of 60, annual cartridge/replacement cost of 80, time horizon of 5, the calculation works out to 1,940.00. Nudge the inputs toward your own situation and the output recalculates instantly. The defaults are meant as a starting point, not a recommendation.

The levers in this calculation

The inputs — Bottled Water Monthly Spend, Filter System Upfront Cost, Annual Cartridge/Replacement Cost, and Time Horizon — do not pull with equal force. Two inputs usually tip the answer one way or the other. Identify which ones matter most by flipping each value past a round threshold and watching whether the winning option changes.

How the math works

Total bottled spend (monthly × 12 × years) minus filter total (upfront + annual cartridges × years). Break-even in months is upfront filter cost divided by monthly bottled spend. The working is transparent — you can verify every step yourself in the formula section below. No black box, no opaque "proprietary model".

Revisiting the plan

Budgets are living documents. Re-run this whenever income changes, housing changes, or you notice a recurring overrun in a category. A budget from two years ago is probably already wrong.

What this doesn't capture

Budgets are snapshots of intent. Real spending includes irregular costs: birthdays, one-off repairs, the occasional bad week. Tracking actual spending for a month before fixing any budget usually reveals 10–20% that didn't make the original plan.