2004 530l , left widow open , big puddle splashed onto dash , car completely dead , no power to anything , tried a boost ,no help ,?

You may have had a big enough short it fried either the mega fuse or a fusible link, especially if water ran onto the underdash fuse box. First get all the water out, it's a lot of work but pull the fuse box and make sure the area behind it is dry, if the backside where the fuses plug in gets wet it can corrode quickly. Then go through all the fuses looking for blown ones, pop the hood and go through that fuse/relay box too, then check the fusible links are still intact. Battery may need to be recharged as well.

of the floor is soaked especially on the passenger side there is electrical connections underneath the carpet. Being that there's a lot of foam and very thick carpet it holds water and will send the cars power to ground also killing the battery. You may even be able to put a voltmeter on the wet carpet and you'll see there's some voltage when the battery is not dead