Carl,

I think that dilution of the pool water with filtered or bottled water (i.e. water that doesn't have chlorine or monochloramine in it) should work for all test methods, including DPD. It simply dilutes all pool chemicals that are in the water and this is done before any testing is done (i.e. before even the powder gets added). I don't think the DPD or any other chlorine test depends on the other pool chemicals being at a certain level to be accurate (CH, TA and CYA).

This link to the "Potential Interferences" section for one of the Taylor DPD tests says "Chlorine levels > approx. 10 ppm may bleach out indicator; to prevent, dilute sample with DI water as necessary and retest." So I think dilution is OK for this test.

Richard