Bottled water, a delivered cooler, and a filtered tap can all look cheap when you read the price on the label. The fair comparison is cost per gallon, counted over the same period, for the same amount of water you actually drink and cook with. This guide shows you how to build that number for each option so you can compare them directly.
Start with your own usage
Before you look at any product, write down how much drinking and cooking water your household uses in a typical week. Count people, not rooms. Include coffee, tea, ice, pet water if you use the same source, and any baby formula preparation if that applies to you. Your weekly total is the number every other figure gets multiplied or divided by. If you guess, use a slightly higher number so you do not underbuy.
Price the delivered and bottled options in full
For bottles or jugs from a store, note the price per container, the container size in gallons, and whether you get a discount for buying in quantity. Divide the price by the gallons to get a per-gallon figure.
For a delivered cooler, the sticker price is only part of the cost. Ask about these items and write each one down:
- The price per refill jug and the jug size
- Any monthly service fee, delivery fee, or minimum order
- The cooler rental or purchase cost, and whether you return it or keep it
- Any deposit on jugs or on the cooler, and the terms for getting it back
- How often they deliver, and whether you must be home or leave a spot for the jugs
Add all of those to the monthly total, then divide by the gallons you actually receive in that month.
Price the filtered option in full
A filter has two costs: the unit and the replacement media. Look at the unit's purchase price, any installation charge, and whether it needs electricity. Then look at the replacement cartridge or filter and check three things on its listing or packaging:
- The rated capacity, usually stated in gallons
- The replacement interval, usually stated in months
- Which of those two limits is reached first
Divide the replacement cost by the rated gallons to get a cartridge cost per gallon. Then spread the unit's purchase price across the number of gallons it will likely produce before it is retired. Add the two together for a filtered cost per gallon.
Check the assumptions that move the number
Most surprises come from a few assumptions, so check them before you decide:
- Rated capacity versus your use. If your household uses more water than the rating assumes, the cartridge will run out in weeks rather than months, and your cost per gallon rises. Ask the seller to put the rated gallons and the replacement interval in writing.
- Water that is discarded. Some point-of-use systems send part of the incoming water to a drain during filtering. If that applies, the water you pay for is more than the water you drink. Ask what share of incoming water becomes usable output, and count the waste in your figure.
- Electricity and drain use. If the unit runs on power or needs a drain connection, add the ongoing cost of both. Your own electric and water bills are the source for those figures, not the seller's brochure.
- Your time. Store runs, jug changes, and cooler swaps take time. Count it if it matters to you, and leave it out if it does not, but be consistent across options.
Put the three options on one sheet
Make a simple table with one row per option. Use the same columns for each: unit or setup cost, monthly running cost, gallons per month, and cost per gallon. Compare the cost per gallon first, then the monthly total, then the upfront cost. A low cost per gallon with a high upfront price may still pay off if you keep the unit for years, while a low upfront price can hide high replacement costs.
Decide what the water has to do
The cheapest per-gallon option is only the right choice if it meets your need. If you are buying filtered water because of a specific concern in your supply, the right question is whether the product is listed for that concern, not only how much it costs. Matching the listing to your own water results is covered elsewhere on this site, and the rating method behind our grades is explained on our methodology page at https://stcharleswaterratings.com/methodology.html. For health questions about your water or your household, talk with your doctor or local water provider rather than relying on a product listing.
Once you have the numbers, choose the option with the lowest cost per gallon that also meets your taste, storage, and safety needs. Write down the figures and the date you did the comparison, then recheck them in a year, since delivery fees, cartridge prices, and your own usage can all change over time.