Not Enough Water in Cities: Skylines

You need to have enough water being pumped, as well as sewage. Note the consumption is less than capacity in both water and sewage, seen here:

You also need to make sure your pipes are connected to the buildings, denoted by a darker blue coloring in the water view, seen here:

If either of these are not true, you will see the No Water notification pop up on a building.

My answer to you is 11 months too late, but I hope this'll help others as well. My problem was that I had two different places for sewage and water pumping and I hadn't connected two of those places. That's why people in other island were complaining about not having enough water in their buildings.

For future reference— Another possible cause for buildings not getting water even when there is sufficient number of pumps and sewage and the pipes are all connected—- check your Budget. If your water budget is set too low that can cause insufficient water supply in spite of everything else being set up correctly.