Take some water to your local Co-operative extension agency. They can give you the PPM of salt.(the town water supplier should have this too) Really, if it would bother your plants, it shouldn't be that healthy for you to drink.
Maybe time to invest in a faucet filter.
kevin

I suspect that it needs iron. In AZ, we have very alkaline soil and J.sambac thrives in ground. My susp is that when the PH is very alkaline then iron becomes less available to plant. so we use iron and epsom salt periodically to our plants.

Is there any particular form in which iron should be supplied? Thanks!

I would love to know the answer to that question too, schiang68. I bought Schultz Bloom Plus 10-54-10, with chelated iron, managnese and zinc and have been using that. So far so good, but then again I've only been using it for almost 1 month. Will this be suitable for my sambacs? I have Maid of Orleans, Confederate(although not a sambac) and Belle of India. Thanks,

GH

Use chelated iron which you can buy from near by nursery. This will help the roots to absorb oxygen and help the growth.
Follow the instruction on the packet.
Once the plant shows healthy growth feed some phosphate.

yes. Chelated iron you can buy anywhere incl HD etc. Once or twice a year add epsom water which helps with absorption of the nutrients.

I flushed the pot with excess water and then gave it iron. Updates to follow when (and if) any visible changes occur. Thanks for all the advice!