He said the 2010-12 drought would happen again but it was "the most collegiate drought" ever because the National Drought Group working with industry bodies became a "sense of community" and 72 per cent of consumers surveyed understood why there was a water shortage in April 2012 even though it had rained so much.
He said education on water resource is important because "we need a debate on resilience" - how much we can afford to supply more water.
He said population growth would exacerbate the problem as would climate change.
Growers can extract 20 cum without a licence if they are in an area with underground water, he reminded delegates.
Bishop added that he expects to see a vast increase in desalination plants over the next two decades boosting numbers from the current single site to up to 10 sites.
HTA business development director Tim Briercliffe said a new HTA working group involving members, Environment Agency representatives and water companies is to work out a longer-term plan for the industry and advise water companies and Government on phasing of restrictions, drip irrigation, communications to consumers and water efficiency in landscaping.