The excessive content of heavy metal ions in water has attracted increasing worldwide attention due to the potential harm to human health and ecological systems. Therefore, it is particularly significant to research and develop a sensitive and straightforward water quality monitoring method. Here, a dual-network designed hydrogel poly(acrylic acid-co-N-methylolacrylamide)/poly(3,4-ethylenedioxythiophene): polystyrenesulfonate, P(AA-co-N-MA)/PEDOT: PSS, was constructed and used for Fe3+ detection. Compared with previous reports, the P(AA-co-N-MA)/PEDOT: PSS hydrogel has a much more sensitive and convenient detection of immune iron ions (Fe3+), is applied to monitor a trace of over-the-standard (the lower limit of detection is 0.52 ppm corresponding to 0.06 S/m for human health monitor, and the threshold for water quality monitoring is 0.16 S/m). The relationship between Fe3+ content and the conductivity of the hydrogel allows it to integrate with other electron devices to provide an early warning function for Fe3+ in the human body, which would be of great significance to human health monitoring.