What does Gardez L'eau mean?
In the Middle Ages, from about AD 500 to about 1500 people pooped in chamber pots. When people dumped the contents out their window they often warned unsuspecting pedestrians by shouting "gardy loo!" - a term borrowed from the French gardez l'eau, meaning 'watch out for the water'.
below image is from the book Toilets of the World by Morna E. Gregory & Sian James