Water is essential to all life and has a regular use in every kind of spellcraft. Collecting sacred or special waters from various locations and charging them before use just adds to their oomph.
Begin by keeping a couple of small bottles or vials tucked into your purse, glove box, backpack, etc., so you’ll always be ready to collect. Take samples of waters that have meaning to you: for instance, water from wells or springs, samples of rivers and oceans visited, rainwater that falls during powerful storms, or melt from the first snow. I collected a piece of ice from a glacier during a trip to Iceland!
To charge your waters, let the jars sit out under the desired conditions (direct sunlight, full moonlight, lightning storm, etc.), particularly on significant dates or during specific astronomical alignments.
Bottle each water and label carefully (because they all look alike). Use them to add strength to your spells and potions.