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San Antonians are living on borrowed money.No, seriously. We have the highest credit-card utilization rate in the country, according to a new study by loan broker Lending Tree's CompareCards unit. The Alamo City's rate of 35.1 percent is significantly higher than the average of around 30 percent.That percentage — essentially the balance of your credit-card debt to available credit — is important because it's one of the biggest factors in determining your credit rating. Financial experts recommend keeping it below 30 percent.So, why does San Antonio have such a high rate?Like many of our woes, it comes down to personal income."With a few exceptions, most of the cities with the highest utilization rates were among those with the lowest household incomes, while higher income cities tended to have lower rates," Lending Tree's report points out.In other words, when you don't earn much in the first place, it's hardto rely on credit when financial emergencies come up.In Bexar County, 15 percent of households fell under U.S. poverty guidelines, but another 36 percent perpetually teeter at the edge of financial crisis, according to a recent study by the United Way.The bottom line is it's hard for families to be financially healthy when they're starting at an extreme disadvantage.