What this calculator does
The Tap Water vs Bottled Water Calculator shows you exactly how much money you spend on bottled water and how much you would spend drinking the same amount from your tap. The difference is your potential savings — often surprisingly large over a year. Currency is shown in dollars but the math works with any currency as long as you stay consistent.
How to use it
Enter how many bottles you drink per day and the price of each bottle. Then enter how many liters of tap water you would drink per day and your local tap water price per cubic meter (1 m³ = 1,000 liters; this figure is usually on your water bill). Finally choose the number of days — use 365 for an annual comparison. The calculator returns your total bottled cost, total tap cost, and the savings.
The formula explained
Bottled cost is simply bottles × price × days. Tap cost requires a unit conversion: water utilities bill per cubic meter, so liters per day are divided by 1,000 to get cubic meters before multiplying by the tap price and days. Savings is bottled cost minus tap cost.
$$\begin{gathered} \text{Savings} = \text{Bottled Cost} - \text{Tap Cost} \\[1.5em] \text{where}\quad \left\{ \begin{aligned} \text{Bottled Cost} &= \text{Bottles/day} \times \text{Price/bottle} \times \text{Days} \\ \text{Tap Cost} &= \frac{\text{Liters/day}}{1000} \times \text{Price/m}^3 \times \text{Days} \end{aligned} \right. \end{gathered}$$
Worked example
Suppose you drink 2 bottles a day at $1.50 each over 365 days: bottled cost = $$2 \times 1.50 \times 365 = \$1{,}095$$ If you instead drink 3 liters of tap water a day at $2.00 per m³: tap cost = $$\left(3 \div 1000\right) \times 2.00 \times 365 = \$2.19$$ Your savings = $$1{,}095 - 2.19 = \$1{,}092.81 \text{ per year.}$$
FAQ
What is the tap water price per m³? It is the unit rate your water supplier charges; check your water bill. Typical rates range from $1 to $4 per cubic meter.
Why is tap water so cheap here? Because 1,000 liters cost only a few dollars, even heavy daily drinking adds up to just a few dollars per year.
Does this include filters or reusable bottles? No — it compares the raw water cost. Add any one-off filter or bottle cost separately if you want a fuller picture.
