I'll be in Lanzarote in February. I've been there in high summer when of course it was very hot but what's the sea temperature like in February?
About 18 degrees Celsius, give or take:
And that website seriously hurts my eyes.
Somewhat more readable, but not giving historical details:
Most of the islands are pretty similar in climate, but Wikipedia has a great chart for temperatures of Gran Canaria and Tenerife, indicating that the average high in February is around 21 degrees Celsius, the mean temperature for the day is 18 deg, and the average low is 15 deg. You can also expect 1 in 8-10 days to have rain, on average.
For more specifically Lanzarote details, we had to hunt through the Agencia Estatal de Meteorología - the metereological agency used as a source for the above Wikipedia data. And yes, they have a climate page on Lanzarote.
This indicates that 17.5 is the daily average, the average high is 21.2, the average low is 13.9 and in terms of rainfall, you can expect 14mm over 3 days of the month, on average.
For the ocean, we have to go to different websites. I'll provide three: