Dry during sex

Recently my vagina gets really dry during sex and the friction hurts :( My partner lasts very long (40mins+) and I really enjoy the long sessions but my vagina just starts getting dry in between now. He stops when I start getting dry because he is afraid of hurting me but I feel a bit disappointed that he has to cum by hand.
I'm 25, not taking any medications or treatments & I love my partner to bits. We tried water based  lube but it dried out as well. Besides not drinking enough water I'm not sure why this is happening?? Any advice?