Possible Clues:

• 'We shall shortly come at the double. Fancy that, now! (4,4)'
• "Oho!"
• Two sources of surprise
• Wells created this? Fancy that!
• We shall come at the double for the water. Fancy that!
• Both O.K.? Just fancy that!
• Who'd have thought that a couple of holes could make one twice as healthy!
• Surprise expressed at sources of drinking-water
• Repeated expression of surprise
• Goodness me, that makes one twice as healthy