Flash loans are a DeFi primitive that allow users to borrow large amounts of capital without collateral, provided the loan is borrowed and repaid within a single atomic transaction. We ask how this form of on-demand, uncollateralized funding affects market liquidity and execution quality in automated market makers. Exploiting the token-level rollout of flash-loan eligibility on Aave as a natural experiment, we show that flash-loan introduction leads to a pronounced and persistent increase in Uniswap V1 liquidity: executable depth, total value locked, and trading activity rise relative to matched control pools, while slippage and volatility do not deteriorate in a sustained way. Using transaction-level classifications and high-frequency panel regressions, we further show that flash-loan intensity is positively associated with subsequent depth and TVL, with effects concentrated in large debt-restructuring and arbitrage loans. Overall, our evidence suggests that flash loans operate primarily as a liquidity-enhancing funding technology that deepens markets without worsening short-run execution quality, while reallocating risk toward passive liquidity providers.