Re: How do different types of water affect the growth of philodendrons?

To find specific studies involving philodendron, you would need to search the 
horticultural literature at a college library using an online database such as 
Agicola or books such as Horticultural Abstracts. 

In general, plant growth declines as the salinity (salt concentration) of the 
irrigation water rises above a certain level which varies depending on the 
salinity tolerance of the species. Other potentially toxic substances in water 
include boron, fluoride, chlorine and sodium. Water from a water softener is 
usually harmful to plants because of its sodium content.

Tap water often contains essential nutrients for plants such as sulfate, 
potassium, calcium and magnesium so tapwater may be better than distilled water.


Reference

Hershey, D.R. 1993. Evaluation of irrigation water quality. American Biology 
Teacher 55: 228-232. (your school's biology teacher may subscribe to American 
Biology Teacher)