Table schema:
CREATE TABLE table_name_69 (latitude INTEGER, pop__2010_ VARCHAR, water__sqmi_ VARCHAR, longitude VARCHAR)

Question: What is the highest latitude when there are more than 0.518 square miles of water, a longitude less than -99.830606, and a population of 18?
SQL: SELECT MAX(latitude) FROM table_name_69 WHERE water__sqmi_ > 0.518 AND longitude < -99.830606 AND pop__2010_ = 18