Use only bottled water, Erikli or Nestle are low sodium but most of the others will be ok anyway. At 15 weeks I would boil it first, let her have it cool but not too cold.
I lived in Turkey when my dd was a baby and I BF her but I also gave her water when it was hot. If you have a feeding routine and she seems like she wants milk in between try water first, or if you feel thirsty yourself just offer it to her. It will be hot so she may like to sip on water a lot.
Thanks we're going to Foca. I've got a cup and a bottle so hopefully she'll take water from 1. Shes BF but seems to like drinking water off her hands so hopefully she'll take it! Worst comes to worst I'll use the Calpol syringe I think.