There are at home tests for testing water for E Coli.
You can buy the E Coli at home test kits through Amazon or other places online and they are pretty cheap and they are good to have around.
You can test your water for E Coli but there's no way to test food for E Coli so if you suspect that the E Coli is in some food then throw it out and do not risk getting E Coli infections or food poisoning.
If you think you've gotten E Coli from anything like water, food etc then you will need to go to the doctor and have a stool sample taken which will then be sent off to a lab for testing.
Most cases of E Coli in humans are not deadly and the symptoms of E Coli typically last around 5 to 10 days.
People with mild symptoms of E Coli usually recover on their own without treatment but it's a good idea to go to the doctor to get tested.