Not to give you more bad news, but I found teh same with the avent. It can take a few goes to see which teats are right. I had a few girlfriends lend me different bottles and we also found that hte tommee tippee closer to nature ones were best. He is still on the newborn teat (1 I think) at three months.

About the water... I think that was a thing in our mothers generation to give water. The nurse that ran my mothers group said something very sensible which was basically if they are thirsty enough to have water they are thirsty enough for breastmilk / formula. The water in the formula will keep your bubba perfectly hydrated. Just keep an eye on enough wet nappies and you'll be fine.

You can add Infants Friend straight to the bottle or give it straight out of the dropper.