I will just add these quotes from Morphett and Tolley to clarify some reasoning behind the weekly water requirement figures in my post above.
"The roots are concentrated mostly in the top 30 - 50 cm of soil.
Trees perform best with even moisture in their rootzone from September
through to April.
( again that is from spring thru autumn down under. pagnr.)
Watering needs will normally vary from nil in winter, to hundreds of litres
per week in mid summer.
Remember that regular watering from flower bud formation through to
final fruit set is important to retain a good crop.

Water in the early morning or at night, especially during summer.
Watch the weather forecasts and water to anticipate higher temperatures.
Feel the leaves during hot days. If they are cool to touch the tree is
getting adequate water. If they feel dry or '' leathery '' they need water.
( the "feel" test is the same as in container trees )

Caution !! The most common cause of damage and decline in citrus is
"wet feet " due to poor drainage and/ or overwatering.
Citrus tree roots need air as much as water. A constantly wet soil drives out air and suffocates the roots. "