Hi dear, well maybe (im not sure) but i had 2 times this problem ... 1 with my 3th gen lude and 2 with my ex-gf integra you may have 2 things,

1: Oil getting in your spark plugs (white, clean smoke)
2: Water Pump (white hot very hot smoke)
But in the way that you're telling (your wather going low) you may check your hoses or even make sure if it's really your water pump, when i had the smoke coming from under my car, it was a little hose that my mechanic charged me $30.00 to replace ,, (i was so paranoid thinking that i was going to spend 200 250 for the whater pump replacement , LOL
Oscar