Always use distilled or deionized water for watering a lead-acid forklift battery. Never use tap water, bottled drinking water, or any other fluid. Using the wrong water type is one of the most common and costly mistakes in forklift battery maintenance.
Why Tap Water Damages Forklift Batteries
Tap water contains dissolved minerals and salts such as calcium, iron, magnesium, and chlorine. When you add water to a battery, these impurities remain behind as the water evaporates, building up on the battery plates over time.
This buildup causes:
Reduced battery capacity and performance
Increased self-discharge rates
Accelerated plate corrosion and degradation
Shortened battery lifespan by up to 50%
Distilled vs. Deionized Water – Which to Choose?
Both distilled and deionized water are purified and free of the damaging minerals found in tap water. The choice often comes down to cost and availability.
Water Type Description Key Points
Distilled Water Purified through boiling and condensation Safest and most recommended choice; typically more expensive than deionized water
Deionized (DI) Water Purified by removing dissolved minerals and salts Perfectly suitable; often more cost-effective for industrial use; can be produced on-site with a deionizing system
For some operations, high-quality deionized water has been shown to help maintain better battery capacity over many charge cycles compared to distilled water.
Best Practices for Watering Lead-Acid Batteries
When to Water
Water after charging, never before – Electrolyte expands during charging; adding water before charging can cause boil-overs and acid leakage
Allow battery to cool first – Adding water to a hot battery can cause thermal shock
Check water levels weekly – or every 5–10 charge cycles
How to Water
Clean the top of the battery before removing caps to prevent dirt from entering cells
Remove vent caps and inspect electrolyte levels
Add distilled or deionized water until the level reaches the fill well indicator
Never overfill – leave room for electrolyte expansion during charging
Replace vent caps securely after watering
Never add acid – only water should be added to lead-acid forklift batteries.
Summary
Forklift lead-acid batteries require distilled or deionized water to maintain proper electrolyte levels. Tap water contains dissolved minerals that accumulate on battery plates, reducing capacity and lifespan by up to 50%. Distilled water is the safest and most recommended choice; deionized water is a cost-effective alternative. Always water after charging, allow the battery to cool, and use only purified water. Never use tap water, bottled drinking water, or any other fluid. Regular watering with the correct water type extends battery life and reduces total cost of ownership.