at how many microns of vacuum does water boil?

Question

tempature was approx 90 deg. F

Answer 1

A liquid will boil when its vapor pressure at the given temperature equals the [atmospheric] pressure above the liquid.

I could not find a vapor pressure value of water at 90 degrees, but,
At 86 degrees F, the vapor pressure of water is about 31.8 mmHg.
If you lower the pressure above water to 31.8 mmHg at 90 degrees F, the water will boil.

31.8 mmHg is about .042 atmospheres.

Answer 2

90 F is approx 32 C. At 32 C the vapour pressure of water is 4.7582 kPa. A standard atmosphere is 101.325 kPa. So its 0.047 atmospheres or 35.7 mm of mercury.