Winter is the defining stress
Across Illinois, incoming water can fall into the 30s and low 40s Fahrenheit in January and February. Heaters must raise that water much further than in summer, so tanks recover more slowly and tankless units deliver less flow at full temperature. Households that run short only in winter usually have a tank that is borderline for their size, not a broken one.
Basement installations are the norm in Chicago and most older Illinois cities. That brings two common issues: drafts from basement windows blowing out pilots, and gas heaters venting into old chimneys that no longer draft properly after a boiler or furnace upgrade.
Water across Illinois
Chicago and many northern suburbs draw from Lake Michigan, which is moderately hard. Communities farther from the lake often rely on groundwater from deep aquifers, which can be considerably harder and sometimes carries iron. Downstate cities draw from rivers, reservoirs and wells, with hardness that varies from city to city. Where water is hard, annual tank flushing and yearly tankless descaling pay off in heater life.
Licensing, permits and safety
Illinois licenses plumbers through the Department of Public Health, and Chicago adds its own registration and permit requirements. Most municipalities require a permit for water heater replacement. State law also requires carbon monoxide alarms in homes with fuel-burning appliances, which includes any gas water heater.
Typical repairs in Illinois run $150 to $650. A standard 40 to 50 gallon gas tank replacement usually costs $1,500 to $3,500, with Chicago toward the upper end. See water heater replacement for details.
Choosing your city
Each city page below covers the local water supply, common problems there and notes on permits and prices.