When pesticides r used in crops they mix with the water and enter the food chain.
when the stored water is used by humans pesticides enter the in the body of food chain.
Well , When pesticides are used to protect crops from insects or for a good yield of crops . Then this harmful chemicals remains on the crops.

And we human beings are a part of this food chain . We depend on producers and we're the consumer who consume this plants which is harmful to us , When we intake this as a food . Therefore ; through this way pesticides enter the food chain and subsequently it affects the human body .