• The minimum well yield requirements for approval of a
domestic water supply is a state regulation that has been in effect since 1981.
The state regulation requires that new well systems must be able to yield at
least 1 gallon/minute over a six-hour period. In addition, new well systems must
be constructed such that they can deliver at least 500 gallons over a 2 hour
period. In other words, lower yielding wells must be drilled deep enough to
provide a reservoir of water available for immediate use.
• A minimum well yield requirement for property conveyance
has been in the Baltimore County Code since 1980. The County Code also requires
that domestic water supplies yield a minimum of 1 gallon/minute, however, the
buyer of an existing property has the right to accept a yield less than I
gallon/minute. In addition, there is no storage requirements for existing wells.
A yield test, conducted to determine the well yield, is valid for three years.
• These laws are intended to provide reasonable assurance
that residents of properties served by private water supplies have adequate
water supplies for typical domestic purposes. They are not a guarantee of water
Theoretically, the minimum well yield (I gallon/minute)
equates to 1,440 gallons/day, which is over 4 times the average consumption for
a family of four (300 gallons/day or 75 gallons/day/person).
DEPRM has recorded well replacement statistics in Baltimore
County since 1989. The data indicates that each year approximately 165 wells (or
<1 % of the 30,000+ wells on record) are drilled to replace a previously
existing water supply. This includes new wells drilled to replace substandard
water supplies such as hand dug wells and springs. The number of wells drilled
per year to replace a well due to "insufficient yield" is
It is DEPRM's experience that most of the replacement wells
drilled due to "insufficient yield" are discovered when the property
owner decides to sell the house and is required to conduct a yield test. The
reason for this becomes evident if you consider the average consumption for a
family of four (300 gallons/day) equates with a yield less than 1/4
gallons/minute. In other words, the minimum yield requirement of a 1
gallon/minute acts as a conservative estimate for most domestic users.
• While it is not uncommon for a well yield to exhibit
seasonal variation, there is generally not a wide fluctuation over the lifetime
of a well. The ability of a well in bedrock aquifers to produce water is
dependent on the number and size of fractures intercepted during drilling.
Occasionally, wells may "go dry" due to drought conditions, or natural
siltation (clogging) of the water bearing fractures.
• Some formations are known to be "good
producers" due to the highly fractured nature of the rock, however, there
remains a possibility of drilling a "dry hole" if suitable fractures
are' not encountered during drilling. In general, it is more likely to drill
higher yielding wells in valleys or drainage swales than it is on ridge tops.
• Water pressure at the tap is not necessarily dependent on
well yield. Proper sizing of the well pump, pressure tank, and distribution
lines by a licensed plumber will ensure adequate pressure for the user.
If you have additional questions or want further clarification contact
Baltimore County's DEPRM at 410-887-2762.