Thank you philodelphi and peeaanut, very good of you. 
@ philodelphi - I use a SplashArt drop controller from Phototrigger, dropping water into a very large Brandy glass (ah, those were the days). About 4-5 inches behind the glass, I place a photograph of the subject, illuminated by 2, or sometimes 3, Yongnuo 560-iii speedlites set to low power and fired by a Yongnuo RF-603C trigger on the camera hot-shoe. Sigma 105mm Macro, ISO 100, f/16.
To have the refracted image of the subject the right way up, the subject must be upside down - if you see what I mean!
@ peeaanut - You are right, focus can be very tricky! My method is to lay a hacksaw blade across the glass, positioned so that a drop hits the blade - then focus via LiveView x 10 on the teeth of the blade, i.e. a millimetre or two in front of where the drop actually strikes. Works pretty well on most occasions.
Sony A7Rii | FE 4 16-35 ZA OSS | FE 2.8 35 | FE 24-240 |OM Zuiko 24 2.8 | MD 50 1.7 l MD 35-70 MACRO 3.5 | MD 135 2.8 4x4 | Sigma 150-600 (C) | MC-11
Sony A5100 | PZ 16-50 | E 2.8 20 | Sony rx100iii | Sony rx10iv
EOS 6d | EOS 40 STM | EOS TS-E 90 | Sigma 50 2.8 EX DG Macro | Sigma 105 EX DG Macro | Sigma 150 EX DG Macro | FD 300 2.8L
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