True, but lemons could get awfully expensive to acidify your water on an ongoing basis. You can use any type of vinegar - I've been using some red wine vinegar lately that I got from my brother when he sold his condo. Hey, it was free! But I do buy the cheapest vinegar I can get my hands on which is "white distilled vinegar" here for correcting the pH of my water.
If the water truly is the problem - and it could be - it might be a great idea for you to buy a test kit - aquarium and pet stores have small ones for people who have fish tanks. Then you can correct the pH of your water to nearly neutral (pH of 7) accurately every time you water your plants.
