The most common method to lower pH or acidify soil is to apply agricultural sulfur. But it is not a fast process as the chemical reaction that causes the change takes time - 3-12 months - to occur, depending on soil type. And not really necessary if growing in containers. Commercial container/potting soil is buffered to have a pH of just around neutral or slightly under, typically 6.5 - 6.9. But you can address nutrient inaccessibility - the primary reason for pH requirements - through fertilization. Or you can use a potting soil formulated specifically for acid loving plants (Dr. Earth, Coast of Maine, EB Stone, Fox Farms all provide such a product).
Hard or alkaline tap or irrigation water can also be neutralized or acidified by using plain old table vinegar, 1 tablespoon to a gallon of water. This is a common practice in areas with hard water and container growing things like blueberries, rhododendrons or Japanese maples.
Q