When I ask this question in a Rain Barrel/Water Conservation Workshop I get an array of answers.
The ocean, Lake Okeechobee, the sewer,the faucet, rivers. Where your municipal water comes from depends on your location and the surrounding natural hydrological system. Our water comes from the Biscayne Aquifer and the deeper underground water of the Floridan Aquifer. Note in Miami Dade County the Floridan Aquifer is mixed with seawater and is considered brackish needing additional treatment (Reverse Osmosis) for our consumption.
How does the Biscayne Aquifer get its water? Rain! Great! It rain a lot in Miami! It's always raining, right?
Yes it rains a lot in Miami Dade County.
Our rainy season approaches, any day now it will start and on average continue thru October. We receive approximately 70% (40")of our annual rainfall in this 5 month span. That leaves 7 months of dry season. Why than do we perceive that it rains a lot in Miami?
When it Rains it Pours.
We do have high rainfall weather events. April 15th produced 5" of rain in our grove. This caused local flooding in many areas of Miami Dade County. Advancing cold fronts can bring several inches of rain in the dry season. Up to April 15, 2015 we had experienced lower than average rainfall for the 2014-2015 dry season. Why? There are fewer cold fronts reaching south and many of the "cool" fronts that do arrive have dissipated their energy and arrive dry.
Where did the 5" of rain go?
Statistically 12% of rain that falls in an urban area will find its way to recharge groundwater resources. The "other" 88% will travel across paved/hard surface areas to the nearest storm water drain/and/or drainage canal. Where does this water go in Miami Dade County? Still going out to the ocean. Ditto for California (remember the two "Pineapple Express" weather events?).
With 5" of rain in one day plants should be good for weeks, right?
Well, NO actually. Water peculates thru our sand based soil right into the aquifer. Have you ever heard a meteorologist describe a rain event as a "slow soaker, just what we need for our lawns"? Too much water at one time washes thru the sandy soil whether the water is from rain or over watering for hours. How long the plants will benefit from rain depends on length of day, temperature and humidity. Call us at the Miami Dade County Extension Office if you have questions!
What if Rainy Season starts late?
Depending on conditions, say record heat, we could face draw down on well fields which are normally at their lowest levels at the end of dry season. The dry season of 2009 was the 2nd driest recorded dry season at the time and we risked salt water intrusion into well fields along the south eastern sector of Miami Dade County. Remember the brief restrictions limiting watering your lawn only once a week roughly south of SW 216th Street?
Climate Change or Not?
Change your focus from predictions and look at recent weather patterns in comparison to historical weather data. Our weather patterns are becoming colder, hotter, dryer, and wetter depending on your location and in some areas in the US it is all of the above. Weather has become more difficult to model and forecast despite advances. What is 100%? Looking at recorded data, ice cores, tree rings and more.
Our climate is changing.
What about Sea Level Rise?
It is happening and you do not need to be a scientist to understand what is happening and how it will affect the Biscayne Aquifer. Sea Level Rise is documented. Well fields are already being inundated by salt water intrusion due to Sea Level Rise and are being taken out of service.
What other issues stress our water resource?
Population! More people = more water. Locally Miami Dade County is now at 2.6 million people and extremely diverse in all measurable areas. Planet wide population exceeded 7 billion March 12, 2012. Peak estimates of now exceed 10.3 billion by 2050. How old will you be in 2050?
Thank you for reviewing the basics
Program Outreach, Rain Barrels and Water Conservation
Water Water Everywhere, Sea Level Rise in Miami
Climate Change Resource Center
NASA Global Climate Modeling
Miami-Dade Sea Level RiseTask Force Report andRecommendations
USGS Coastal Groundwater Systems
The Effect of a One-Foot Sea Level Rise on Saltwater Intrusion in theBiscayne Aquifer in Miami-Dade County, Florida
Ground Water Atlas of the United States: Alabama, Florida, Georgia and South Caroline