How this calculator works
Tap water arrives through a municipal system and is billed by the cubic metre, which is 1,000 litres. Bottled water is billed per litre at retail, often a dollar or more for a half-litre bottle, so the price ratio can exceed a thousand to one. The calculator multiplies the daily amount by the household and the days in a year, splits it by the share bought in bottles, and prices each part at its own rate. The bottle count comes from the volume divided by the bottle size, and the plastic from an average of about 22 grams per litre, the weight of a typical 500 mL PET bottle. Bottle manufacturing emits about 2 kg CO2e per kg of plastic. The comparison does not include the cost of a reusable bottle or a filter, which is small over a year, and it assumes the same volume is drunk either way.
Formula
water per year (L) = litres per person per day x people x 365. bottled litres = water per year x bottled share. bottles = bottled litres x 1000 / bottle size in mL. bottled cost = bottled litres x price per litre. tap cost = water per year / 1000 x price per cubic metre. saving = bottled cost - tap cost. plastic (kg) = bottled litres x 0.022. emissions = plastic x 2.0 kg CO2e per kg.
Worked example
Four people drinking 2 L a day is 2 x 4 x 365 = 2,920 L a year. All of it bottled in 500 mL bottles is 5,840 bottles. At $1 per litre the bottled cost is $2,920; the same volume from the tap at $2.50 per cubic metre is $7.30. The saving is $2,912.70 a year, or $14,563.50 over five years. The bottles weigh 2,920 x 0.022 = 64.2 kg of plastic and emit about 128.5 kg CO2e.
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Frequently asked questions
Is tap water safe to drink in Canada?
In almost all Canadian municipalities, yes. Water utilities are regulated and regularly tested, and boil-water advisories are issued where treatment fails. If you are on a private well, test it annually for bacteria and the contaminants relevant to your area.
What about taste and chlorine?
A filter pitcher or a tap filter removes chlorine and improves taste for a fraction of the cost of bottled water. Letting a jug stand in the fridge for a few hours also lets chlorine dissipate.
Are the bottles recycled?
Most PET water bottles are recyclable, and deposit systems recover a high share in some provinces, but national recovery is well below half. A recycled bottle still used energy to make, collect and reprocess, so refilling is better than recycling.
Is bottled water sometimes necessary?
During a boil-water advisory, a disaster or when travelling where treatment is uncertain, bottled water is a reasonable choice. The comparison here is about everyday use where tap water is safe.