Groundwater Balance & Draft vs Recharge

The balance is simply recharge minus draft: balance = annual recharge − annual draft, in cubic metres. A positive balance means more water is replenishing the aquifer than is being pumped out, so the water table holds or rises. A negative balance means draft exceeds recharge and the aquifer is being mined — the water table falls year on year.

It is the percentage of the recharge that is being extracted: stage = (draft ÷ recharge) × 100. At 50% half the annual recharge is pumped; at 100% the entire recharge is used and there is no surplus; above 100% the aquifer is being drawn down faster than it refills. It is the single most important indicator of how hard an aquifer is being worked.

They follow the standard groundwater assessment bands. Safe is a stage at or below 70% — there is ample headroom. Semi-critical is above 70% up to 90% — caution is needed. Critical is above 90% up to 100% — close to the limit. Over-exploited is above 100% — draft exceeds recharge and the resource is declining.

The category guides what you can do. In safe areas new wells and expanded irrigation are generally fine. In semi-critical and critical areas, fresh abstraction is restricted and recharge measures are encouraged. In over-exploited areas new wells are usually banned and the focus shifts to demand management and artificial recharge, because the aquifer is already in deficit.

Use the same volume unit for both recharge and draft — cubic metres (m³) is standard, but hectare-metres or million cubic metres work just as well as long as both inputs match. The balance comes out in that same unit and the stage percentage and category are unit-independent because they are a ratio.

Recharge is the water that reaches the aquifer each year from rainfall infiltration, return flow from irrigation, canal seepage and recharge structures. It is normally assessed with the rainfall-infiltration-factor method or a water-table-fluctuation study over a year. Use the assessed net annual recharge for your block or watershed for the most meaningful result.

Draft is the total volume pumped out in a year — irrigation, drinking water and industrial use combined. It is usually estimated from the number of wells, their average discharge and hours of operation, or from energised pump-set data. Sum every source that draws from the same aquifer so the balance reflects the true demand on it.

Not by this definition — the stage and the balance are two views of the same ratio. If draft is below recharge the balance is positive and the stage is below 100% (safe, semi-critical or critical). Only when draft exceeds recharge does the balance go negative and the stage cross 100% into over-exploited. The category and the sign of the balance always agree.

No — it is a quantity balance only. An aquifer can be quantitatively safe yet have salinity, fluoride or nitrate problems that make the water unusable, and those are assessed separately. Treat the stage and category as a measure of how much water is left, then check quality before relying on a source.

They are exact for the numbers you enter — the arithmetic is straightforward. The accuracy depends entirely on your recharge and draft estimates, which carry real uncertainty in the field. Use assessed block-level figures where you have them, and treat the result as a planning indicator rather than a guarantee.