If I understand the question, I don't believe you will see a significant increase in pressure at ambient temperatures. Lets assume the temperature is 70F, at that temperature water turns to vapor (boils) at 0.36 psia (that's a vacuum of about 14.3 psig, or 29 in of Hg). Therefore, if you pump the system down to 29 inches some of the water will turn to vapor until the partial pressure of the water vapor reaches the equilibrium pressure. At that point the water should stop turning to vapor until the system is pumped down again. IMHO, the only way the pressure would continue to increase would be to increase the temperature. Is that what you were asking?