How do you know of your waters have gone?

I got out of bed this morning and was wet. It has soaked through my underwear and Left a damp patch on the sheets. I went to the bathroom and blew my nose and felt like I'd peed myself (luckily I was already on the toilet). It was like a hush but it doesn't smell like urine and is very pale almost too clear for mucus.  Could this be some sort of late pregnancy incontinence or could my waters have gone? I've not noticed my mucus plug or any blood, I'm only 36wks....I have a midwife appt this afternoon do am going to ask her but would appreciate any insights as to how you know it's your waters or just fluid.