Various dermatological conditions have been assoctiated with itching and erosion of skin. The areas need to be observed under a dermatoscope to look for changes in colour, texture, hair follicles and others. For the itch, any anti histaminic medicines both orally and topically, also topical steroids (creams) would help. Also mention if the source of water is same everytime you re experiencing the itch upon exposure. It could be a fungal infection as well if the water is contaminated. Consult your dermatologist to know exactly what condition you are suffering from. We ll then help you understand the disease and guide you accordingly.