Look in the kitchen, bathroom/s and laundry for dripping taps and washing machine and dishwasher connections and damp patches on the wall.
Also check you toilet cistern for leaks by placing a few drops of food colour in the tank. Without flushing it, look for colouring in the toilet bowl. If it is getting through you have a leak.
Look at outdoor garden taps/hoses, garden reticulation (including sprinklers), automatic solenoids and manual isolation valves along with any exposed pipe work.
Check hot water systems and air conditioning units.
Also look for damp and unstable brick paving and garden areas that may be moist and greener than expected.