There are two major forms of hydroponic production systems:

1. Recirculating hydroponic systems

2. Flow to waste hydroponic systems.

Both recirculating systems and flow to waste have their pros and cons, however, and today we're going to look at each type of system.

In a recirculating hydroponic system, water is continuously recaptured and recirculated. The solution is injected with more fertilizer as needed, determined by regular nutrient testing.

These hydroponic systems discharge water every one to three months because nutrients become unbalanced or metals, such as aluminum or copper, accumulate. Plants won't take up heavy metals or excess nutrients in high quantities, so it is not necessary to keep them in the system.

Water loss and costs are very low in a recirculating system, especially when compared to traditional agriculture. Evapotranspiration is the largest source of water loss, followed by irrigation leaks. There are additional costs associated with tracking and replacing nutrients. Beginning farmers may find rebalancing nutrients difficult or beyond their skill level.

In a flow to waste system, the solution is injected with fertilizer just as in a recirculating system. Then, instead of capturing runoff water, the solution simply drains away after it has been fed to the plants. Any water not used by the plants is lost.

This doesn't always mean that a lot of water is wasted, however. When set up properly, flow-to-waste systems can be very efficient, only draining a few gallons a day. Drained solution can also be used elsewhere, such as for seedling systems or field crops.

Flow to waste systems are also easier to manage, since there is no need to rebalance the system or constantly test for nutrients. Logistical costs are comparatively inexpensive. 

Almost all aquaponic systems are recirculating. Nutrients in an aquaponic systems are more valuable and difficult to replace. Many nutrients in an aquaponic system are stored in organic matter, which needs time to break down and become available to plants. Replacing lost nutrients in a flow to waste aquaponic system would take prohibitively long.

Bright Agrotech encourages use of recirculating systems. Water is a valuable, finite resource that should be conserved whenever possible.

In our 350 ZipGrow tower recirculating system, we only lose about 1%, or 40 to 60 gallons, of our water daily due to evaporation. Other hydroponic systems lose 7% daily, and traditional agricultural water losses can be as high as 50%.