Water Capacity Requirements

Click here to view the Marin Municipal Water District (MMWD) web pages relative to this topic.

Current Usage

The MMWD currently supplies approximately 31,000 acre feet of water per year to it's 190,000 customer population.
That is an average of approximately 140 gallons per day for each person, or 26 MGD (million gallons per day) total.
Of this, winter use is somewhat less, and summer usage - with outside watering, is somewhat greater. (Summer irrigation uses approximately 30 per cent of the total annual usage.)

Current Capacity

Since MMWD gets essentially all of its water from run-off of rain water in West Marin, our current capacity falls into two categories, the catchment and storage capacity of our reservoirs and the amount of run-off into these reservoirs each year.

The current capacity of our reservoirs is approximately 80,000 acre feet of water, or about 2 to 3 times our annual water usage..

However rain fall, and related run-of, is not constant each year. In fact, while in many years sufficient run-off occurs to overflow the reservoirs, in many years it is insufficient to completely fill the reservoirs. (Click here to see the historical amounts of rainfall by year since 1872 - including three periods of drouth.)

Thus, prudent operations requires that a reserve be maintained for drought years. However, the amount of such reserve is subject to judgment. Quite naturally those who are charged with safe operation of the system are likely to be more conservative in that judgment than those who are not - and may have other motives for their stated judgment.

Future Needs

Marin is not completely developed, with new development requiring additional water capacity.

Additionally, there is the specter that Global Warming may change the rainfall pattern, shifting more rain to the north and causing an increase in the frequency and length of drought periods.

The MMWD currently projects that we have a 3,000 acre-feet per year deficit and that, without additional sources, this deficit will grow to about 6,700 acre-feet per year by the year 2025.

The combination of these factors leads to a need for additional capacity, or water savings, in the future.