Interruptions to the water supply seem to be a common occurrence in the Honor Oak/Forest Hill area. We haven't had any recently* but have had at least three episodes of no water for hours on end (sometimes nearly 24 hours) since moving here. We now keep bottles of it in the shed for emergencies.

I lived in SW London for 23 years and had constant water for all 23 of those years.

*that's really tempting fate, isn't it?