Answer: Since the problem is a sudden one I would suspect an environmental change, with a likely problem being lack of humidity. Once we turn on the heating system, the air inside our home becomes very dry. This lack of humidity can affect plants with the symptoms you described. Setting the plants on a pebble tray filled with water or running a humidifier can help. The heating system can also cause hot drafts, so make sure the plants are not sitting in front of forced air heating vents or atop radiators.
Another possible problem can be a gradual buildup of salts in the potting soil due to using fertilizer. You might try leaching the soil by watering heavily to the point that water is running through the bottom of the pot several times in a row to flush any salts out. If there is any buildup or residue of minerals on the soil surface, remove that, too.
Tap water does not usually cause a problem unless it has been treated with softener chemicals -- these may adversely affect plants. If you have a water softener, use rain water or use water drawn out of the system prior to it running through the softener. Most houses equipped with a softener will have a tap or possibly an outdoor faucet for just this purpose.
One last possibility is that the plants have slowed their growth for the winter and as a result need less water than you have been accustomed to giving them. Make sure you are nto overwatering as a result.
Q&A Library Searching Tips