Water aversion?

Hi
We have 2 Light Sussex hens about 18 months now and moulting.  2 days ago one took a drink from their normal drinkers and after two mouthfuls stepped back in a surprised way.  Stepped up to drink again and then stepped back again as though something hurt her.  She has done this since then.  We phoned the suppliers and after some questioning they suggested it may be her crop but it doesn't feel full and she is taking in food and pooing too.  She is bright in every other way.  We have checked in her mouth all seems fine.  We did give her a few treatments of liquid parrafin as it can't hurt.  The top of her beak is slightly discloured and that has been like it for a while.  She has had white skin appearing on her earlobes for a while now and now the other is also showing this.  My husband thinks its Favus as he's been reading Avoid the Vet, but there are no scabs or other signs. Not sure if any of these things are connected or not.   
Any suggestions would be helpful
thank you

the white on her ear lobes is normal some of my hens got it as they got older. 

I've just read something about acidosis and wondered whether the warmer weather is affecting the water, we do generally add cider apple vinegar. The hen is drinking, but its only half of what she would normally take in, the others are quiet happy and appear unaffected.  We have changed the water, offered it with and without cider apple vinegar and in different containers, could she have got extra sensitive. It suggested using bicarb of soda, has anyone any idea of what quantity? 
Didn't know whether it was worth a try?

We do use plastic containers, I understand that metal ones don't react too well with the ACV mix.  We did try plain water and different containers too, and she still reacted in the same way, but will try crushed garlic and see if that makes the difference. thank you