Water heaters (and chillers) are important in hydroponics to maintain the temperature of your nutrient solution. The exact temperature depends on the variety of plants you are growing but aim to keep your solution between 18-22°C. If your nutrient solution is too cool (below 18°C) it will slow and stunt plant growth - you can raise the temperature of your nutrient solution with a water heater. If your nutrient solution is too hot (above 22°C) the amount of dissolved oxygen in the solution decreases and it also becomes a breading ground for bacteria - you can lower the temperature using a water chiller. The Teco chillers and heaters are built for Hydroponics, and come in a variety of sizes from 150 litres to 1000 litres Teco's have a premium price for a reason: their great performance and warranty. Don't be fooled by a cheaper aquarium chiller - we've found they only last one grow before something goes bad.