According to sigma's website digitonin solubility in water is 5% (w/v) upon heating at 98 C and cooling to room temperature. This solution is saturated with digitonin, which means that if you have something else in solution or lower the temperature precipitation will occur. The only way is to have another surfactant (with more affinity towards water) in solution if you want to proceed with your 1% solution (you could also try lowering this concentration), but I guess you do not want that. 

Have you solve this problem? I have same problem with you now, I don't know how to do.

form this source: https://static1.squarespace.com/static/51cb031de4b08c2dba6581d3/t/51f934dde4b07a7d13fb5c70/1375286493178/Commonly+Used+Reagents.pdf

Digitonin is a steroid glycoside from Digitalis purpurea. It may permeabilize plasma membranes and may form complexes with cholesterol. It belongs to the class of non-ionic detergents and is frequently used to dissolve membrane-bound proteins. At concentrations between 10 - 100 μg/ml, cholesterol-rich plasma membranes are permeabilized only, but not those of organelles. Digitonin is suitable to e.g. isolate the opioid receptors from membranes of rat brains, maintaining the capability to bind different agonisten/antagonists. Digitonin is hardly soluble in either water, chloroform or ether. You may

dissolve 1 g/57 ml in absolute ethanol and 1 g/220 ml in 95% ethanol, respectively. Stock solutions of digitonin (e.g. 10 % w/v or 1 mg/ml) in water or buffer (e.g. pH 7.2 - 7.5) may be prepared by heating (95 - 100°C) or vortexing, until a clear solution is obtained. Digitonin that may precipitate after cooling (+4°C) is removed by filtration. DMSO may be used as well (stock solution 20 mg/ml). Stability of stock solutions: solutions of digitonin may be stored up to one week at +4°C. The capability of digitonin to permeabilize membranes may differ from batch to batch from all suppliers.

Hi,

I dissolve in dmso. My current stock is 20mg/ml