DESALINATION and other big-ticket solutions to Melbourne's water woes threaten to sideline alternatives, as a proposal to drop rainwater tanks is the subject of a row at the highest levels of State Government. - Tanks in doubt - Water estimates wrong - Decision in balance "There are water tank wars going on," a senior Government figure said, describing a debate being viewed as pivotal to the future of Victoria's water planning. "With desalination plants and other water initiatives coming in, the rainwater tank has been singled out as something that may not be warranted in the future," the figure said. As part of the strategic battle in the Government, Australia's foremost scientific expert on tanks has been commissioned to study their potential in Melbourne. The Age has obtained two confidential reports by University of Melbourne systems scientist and microbiologist Peter Coombes, which appear to challenge the Government's big-project direction. Although his reports do not say it, their implication is that an alternative water strategy across Victoria could save taxpayers and home buyers billions of dollars by reducing reliance on expensive public water facilities. In one report he argues that previous simplistic estimates for water volumes generated by tanks in Melbourne are wrong, and badly misjudge the capability of tanks to supplement water supply. Although he refused to comment on the reports, Professor Coombes confirmed his work showed a tank in each Melbourne household could deliver a city-wide 120 gigalitres a year, more than twice previous estimates by water supplier Melbourne Water. His most recent report to Government found that: