Bioequivalence and Bioavailability Forum

❝ […] specific guidelines for water 'consumption' in BE studies

Yes, but only in some guidelines. Moreover, different recommendations for standardization are given.

EU, Australia, and Malaysia:
[…] standardisation of […] fluid intake […] is recommended. Subjects should preferably be fasting at least during the night prior to administration of the products.
All […] fluids taken after the treatment should also be standardised in regard to composition and time of administration during the sampling period. The subjects should abstain from […] drinks, which may interact with circulatory, gastrointestinal, liver or renal function (e.g. alcoholic or xanthine-containing beverages or certain fruit juices).

http://www.fda.gov/cder/guidance/5356fnl.pdf FDA:
Before and during each study phase, we recommend that subjects be allowed water as desired except for 1 hour before and after drug administration […]

Canada:
The administration of […] fluid should be controlled carefully. Normally, subjects should fast for 10 hours before drug administration. A fast means that no food or solids are to be consumed, although alcohol-free and xanthine-free clear fluids are permissible the night prior to the study. On the morning of the study, up to 250 ml of water may be permitted up to two hours before drug administration. […] Two hours after drug administration, 250 ml of xanthine-free fluids are permitted.

New Zealand:
For medicines taken orally, gastrointestinal conditions should be standardised. Subjects should be fasted for at least 10 hours before and 2-4 hours after dosing, or (if more appropriate for the medicine concerned) the dose should be given with or before/after a standardised meal. […] Any fluids taken with the dose should be the same for all subjects.

South Africa:
In fasted studies the period of fasting prior to dosing should be standardised and supervised. All […] fluids taken after dosing should also be standardised in regard to composition and time of administration and in accordance with any specific requirements for each study.

WHO:
Standardization ([…] fluid intake, […], restriction of the intake of alcohol, caffeine, certain fruit juices […] in the time period before and during the study) is important to minimize the magnitude of variability other than in the pharmaceutical products.

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Edit: Link corrected for FDA’s new site. [Helmut]

Malaysia
at least 150 ml fluid
http://www.bpfk.gov.my/pdfworddownload/MSIA%20BEguide.pdf (2000)

Different volumes (between 100 ml and 250 ml) are recommended in some national guidelines.
An overwiew of updated guidelines is given below:

Japan
water between 100 and 200 ml (normally 150 ml)
http://www.nihs.go.jp/drug/be-guide/GL061124_ganryo.pdf (2006, in Japanese)

Argentina
200-250 ml water
http://www.anmat.gov.ar/normativa/Normativa/Medicamentos/Disposicion_ANMAT_1746-2007.pdf (2007, in Spanish)

South Africa
e.g. 200 ml fluid
http://www.mccza.com/documents/2.06%20Biostudies%20Jun07%20v2.zip (2007)