This is a standard problem with all outside water jumps and even a greater problem when a track that has 9 - 48" lanes.
The preferred layout is for an inside water jump but unfortunately many tracks are multi use facilies and an outside jump is needed.
The IAAF allows for some flexablity for the placement.
We had this problem at the 2007 World Championships in Osaka, Japan. The Technical Delegates decided to increase the width of the first hurdle by placing two hurldes next to each other.
I first came across this problem when I served as the Technical Director of the 1998 Goodwill Games. Working with Bob Hersh (then a member of the IAAF Technical Committee and now Senior VP of the IAAF) I measured out a box (alley) start for the first two barriers with the break line on the back similiar to the 800.