Tap water is not universally bad for houseplants, but its quality and composition can vary depending on your location, and this may have an impact on certain plants. Some factors to consider when using tap water for your houseplants are:

1. Chlorine and chloramine: Many municipal water suppliers add chlorine or chloramine to disinfect the water. While these chemicals are generally present in low concentrations, sensitive plants may be negatively affected. You can reduce chlorine levels by letting tap water sit in an open container for 24 hours, which allows the chlorine to evaporate. Chloramine, however, does not evaporate as easily and may require specific water treatments or filters to remove.

2. Hard water: Hard water contains high levels of dissolved minerals, such as calcium and magnesium. Over time, these minerals can build up in the soil and cause problems for some houseplants, particularly those that prefer acidic soil. Signs of hard water damage can include yellowing leaves, stunted growth, and poor overall health.

3. Salt and fluoride: Some tap water may contain elevated levels of salt and fluoride, which can be harmful to certain houseplants. Excess salt can cause root burn, while fluoride toxicity can lead to leaf tip burn and browning.

4. pH levels: Tap water's pH can vary depending on its source, and some plants have specific pH preferences. If the pH of your tap water does not match the preference of your houseplants, it may cause nutrient deficiencies or other problems.

To determine whether your tap water is suitable for your houseplants, you can have your water tested or use a home water testing kit. If your tap water is not ideal, consider using filtered, rainwater, or distilled water for your houseplants. Always monitor your plants' health and adjust your watering practices as needed.