This Shabbos we had quite an experience. Water pressure went at around 11:30 AM, and by 1PM, almost no one in my neighborhood had water. Water came back on at around 10PM. As we drink only bottled water, we had no problem with netilas yadayim when necessary. I brought a bunch of empty bottles down to Rav Berkovits's shul, where in his zechus, the water kept flowing. We had a constant influx of visitors to the shul kitchen to fill bottles... (With the full permission of the Rav and also the one who pays for the water - not us, because we pay a flat rent fee.)
A grizzled Israeli told me that he never had this in the forty years he was in the neighborhood (water gone without advance warning for more than three hours).
Btw, it was HOT HOT in the morning, but for some reason, the heat wave broke at around 11:30AM and it stayed cool until this morning. Hmm...