Can you water lavender too much?
Typically, lavender fatalities occur when the plants are over-watered. Lavender is drought-tolerant, which means mature plants don't need to be watered all the time like your other garden plants. Too much water can leave them susceptible to root rot and fungal disease.
Why is lavender drooping?
On hot days, lavender will droop to conserve water, even if it's not thirsty. It's just a natural strategy to stay hydrated. If you notice your plant drooping but don't think it's overwatered or in the wrong kind of soil, check on it later when the day is cooler. It may very well have perked up on its own.