While it is popular for vegetarians to create models showing an embedded cost of meat production, traditional farmers are too busy farming to create an embedded cost for organic food. But it is high. Organic farms use more water and less efficient pesticides and less efficient fertilizer and that leads to being a high stressor overall, but in a drought-ridden state like California, where organic farming remains popular, it approaches crisis levels.
There are some obstacles that cannot be overcome for California when it comes to water. Environmental lobbyists are too strong to allow common-sense approaches like building more water reservoirs or dumping fresh water into the pacific Ocean but a revenue-neutral tax on organic products would account for those inefficiencies and that would lead to saving water as farmers get more efficient.
Organic farmers and customers truly care about the environment so they will be fine with offsetting the higher demand they place on the environment with money, similar to arguments for cap-and-trade when it came to carbon emissions found a free market would be created around that. Organic farmers who did approve efficiency could sell their water credits to less-efficient organizations, etc.