It's different for everyone, I have read that only 15% of women waters break prior to 'established' labour and the first sign is usually contractions that become more regular and more painful. This is what happened to me last time as well, my waters were broken 30 mins before my son was born. There's also a mucas plug/bloody show, which I didn't have last time but this time didn't mean much as it was 4 wks ago. Try nhs website for more info? :)