What would be the most effective method of reducing the incidence of blood flukes in a human population?

By the use of uncontaminated water

Explanation:

Blood flukes are flatworms that are parasitic in nature. These are also called schistosomes.

If we consider the mode of transmission of the parasites to humans, we find that their transmission occurs in the following conditions -

These parasites enter the human body when a person is swimming in contaminated water. They can also infect the human body if the person drinks contaminated water or eats food that have been washed with the contaminated water.

Thus it becomes clear that contaminated water is the main source of infection of blood flukes so using uncontaminated water and avoiding to be in contact with contaminated water will reduce the incidence of blood flukes in human population.