What are the draw back of using fertilisers? ...
Answers: Fertilizers are salts of a sort and can burn the plant leaves and/or roots if applied within correctly.
Applying the wrong fertilizer may cause the plant to do something excluding what was intended. For instance the homeowner wishes lots of tomatoes so they apply a 20-7-17 fertilizer. They will get lots of top growth (the first number), but few blooms/fruit (the second number) and the plant will enjoy a good root system (the final number)
And yes they can pollute ground water, but it have to be in huge quantity to do this. The average homeowner will not apply enough to contaminate any hose down source. Fert can be applied as close as 3 feet in need harming a flowing (river, creek, etc) marine source.
Hope this helps. :)
Too much can disrupt plants, if you are using them outside, it can run into the ground water