You guys are all making a incorrect assumption. ~ The density of the mix does not change with the addition of water. Problem is the density does change.
I suspect the OP is measuring the concentration (%) using a hydrometer ~ that is inferring the % from the density.
Best the OP add about 1/2 the suggested water & then slowly add more until the required density (%) is obtained.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving