Sterilize canning jars by boiling them in water for 10 minutes. Keep the jars hot until ready to use.
Blanch peaches in boiling water for 30-60 seconds, then transfer to an ice water bath. Slip off the skins using a paring knife.
Halve or slice the peaches, removing the pits.
In a saucepan, combine water and sugar to make a light, medium, or heavy syrup, depending on your preference. Bring to a boil, stirring until sugar dissolves.
Pack peach halves or slices into hot jars, leaving 1/2 inch of headspace. Add lemon juice if desired to help maintain color.
Pour hot syrup over the peaches, maintaining the 1/2 inch headspace. Remove air bubbles by running a non-metallic spatula around the inside of the jar.
Wipe jar rims clean. Place lids on jars and screw on bands until fingertip tight.
Place jars in a water bath canner. Ensure jars are covered by at least 1 inch of water. Bring to a boil and process quarts for 25 minutes (adjust for altitude if necessary).
Remove jars from the canner and let cool on a towel. Check seals after 24 hours. Store in a cool, dark place.