IN the end it will depend on what she is used to and the quality of water where you are in the uk. If the wife is used to bottled water in ph and your tap water is not really good then go for bottled. I came from davao where dumoy tap water is very good quality (still get upset tummy for a day every holiday, but i know its normal). Then i switched to bottled water when i was in dubai but you dont have a choice but bottled water (you can drink tap water but since its desalinated, i think the sodium content is too high). When i moved in scotland, i didnt have to adjust to the water. Just drank tap water from day 1. I guessed if my immune system helped me survive ph then uk water would be piece of cake, lol.
There is no such thing as 'not really good' (drinking) tap water in the UK . It is very very tightly quality controlled... unlike in the Philippines. Any ill-effects after drinking it are likely to be either imaginary, or down to something else.