Water and electronics do not mix.  They never have and never will.  When looking to purchase any laser, look to see how water resistant or water proof the laser is.  

The best construction lasers come with an IP68 rating is a 6 for water and an 8 for dust.  This is a good rating and will work for most contractors any where in the US or Canada.  Many of the cheaper lasers will have no rating at all, and some have a rating of 1 or 2.

No matter what water resistant or water proof number you have, if your construction laser does get wet do not put the laser back in the carry case and close the lid.  If you laser does get wet, dry it off completely before storing it and make sure there is no water in the case.  Doing these small things will extend the life of your laser.

Check out the Chart in the Leica Rugby 810 laser. It shows the IP rating for all the Leica Rugby 800 Series lasers.

Leica Rugby 810 General Construction Laser with Li-Ion rechargeable battery.