I would be extermely careful when prescribing these medications as some of them can prohibit histamine release and cause the condition to worsen.
There are some medicated shampoos out there for dogs and cats to help aleviate conditions such as itchy skin.
There are also dermatologists for dogs and cats that can help diagnose skin allergys and help treat them , If the steriods are not working then please see your vet who is prescibing them as steriods have other side effects that are unwanted and if the medication is not working then it would be best not to continue with these.
Aloe Vera in spray form works with my dogs allergys but it has to be 100% aloe vera and thats my dog not yours but it will not do any harm in trying it.
Please try and rule out what it actually is that is cuasing this reaction, is there something in the water that you do not know about i.e chemicals - please contact your local council they may able to help.
Good luck please let me know if i can be of any help xx