what water? if it's from the tap probably the cause, rainwater only for ericaceous plants.. you can fill buckets from tap and leave a week or so, but tap water(hose) big no no.
If the leaves are yellowing it's probably magnesium deficiency. As Camellias are acid-loving plants, yours will benefit greatly from an ericaceous feed. I'd give it a few fortnightly liquid feeds now and then longer term a granular feed in Autumn. Rainwater is definitley best. I'd also mulch with some ericaeous compost. I have 2 in pots and 1 in the ground and do this every year
Sod the camellia just now- the yellowhammer will be more attractive Sara!
You can prune the camellia later and give it some care once the birds have gone. How lovely to have them. We don't get them up here.