Clean jugs with dish soap and thoroughly rinse to remove all residue.
Sanitize re-used bottles with:
1/4 tsp of plain chlorine bleach for every 1/4 gallon.
( 1 tsp/gallon ratio)
Slosh that solution all around, and again, rinse thoroughly.
Fill the bottle up with your regular water. If the water you fill with does not already have chlorine added, add 2 drops [ save your old medicine droppers] of plain chlorine bleach to each gallon.
Without touching the inside of the rim, or the cap, re-cap your jug tightly.
Date your jug clearly with a permanent marker, and store it in the coolest, darkest place you can find.
This water should be replaced every 6 months though, if you do not use it.