First of all, drinking more water does not cause dilution of hcg hormone.
Chance of pregnancy
is high, if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Ovulation occurs approx 14 days before due date.
Early pregnancy may give negative result. Therefore, if period does not come out within 7 days, then you should repeat the pregnancy test with urine/blood for Beta-hcg to confirm/exclude pregnancy. Check the result and consult with doctor.
Other reasons like hormonal
problem, wt gain/ extreme loss,irregular eating habits etc. are required to rule out if pregnancy test is negative.
Avoid stress,take healthy diets, control body wt and need proper sleep.
If you need further consultation with me,then you can visit http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.