At that age they should be having water. Anywhere between 4 to 6 oz of water a day. Talk to your doctor if unsure. But be careful you don't want to a) overfeed baby by offering too much milk, b) dehydrate baby by not offering water.
@Kali You can’t overfeed a breastfed baby and breast milk composition changes with temperature to increase water content, so offering extra feeds (alongside sips of water) ensures baby stays hydrated. Perhaps the advice outside of the UK also differs in terms of quantity of water that should be offered/consumed.
I second what @Chloe said. For example Italy and Greece they said max 3 oz a day
All babies should get sips of water with every meal once having solid foods. The uk nhs have no limits on water intake for babies as there's no science to show any downsides for large water intake. Therefore it should just be sips of as much water as they want at meals. As already mentioned, they don't require any additional water unless somewhere particularly hot
does she have water with food? all babies need water with solids or they can get constipated and dehydrated. If breast fed they don't need any extra due to hot weather.
If she’s on solids, she should be having sips of water anyway, so if you’re offering it already she won’t need any more than that. Offering extra feeds can help keep her hydrated in the heat. When we went abroad, I offered more water, but it was around/above 30°