Filling Your Pool
The average suburban in-ground pool with a surface area of 25sqm starts off by containing approx 38,000L of water or, by the time Melbourne Water or the local regulatory authorities apply their charges, (approx $4 / 1000L) $150 of water.
Water Loss due to Evaporation
In terms of evaporative water loss – even with solar heating your pool should only lose water in the peak summer season from mid November through to mid March. On average approx 5 – 10mm of water per day or 0.005 – 0.01m of water will be lost off the surface of the pool. This means a total water loss for the period of 120 days x 25 ( sqm ) x 0.005 – 0.01 = 15 – 30cm of water or 15,000 – 30,000L. Whilst this figure seems high its offset by Melbourne rainfall in this period on average of 250mm for the 120 days or approx 9500L of water hence the average in-ground pool will need a net water input of approx 5000 – 20,000L of water for the year or approx $20 – $80 of water.