It is only in the last few hundred years that manmade mikvas
have become so prevalent all over the world. In dry areas
such as Eretz Yisroel there was an ancient need to build
suitable mikvas but elsewhere, where public water is more
common, those needing immersion just used a natural spring or
gathering of water suitable for the purpose.
The first documented outline for the construction of a mikva
comes from the times of the Rishonim (11th To 15th century).
One of the oldest in Europe is found in Cologne, Germany,
dating to 1170 (4930).
In those times, many mikvas were built as follows: A wide
shaft was dug into the ground to below the depth of the
natural water table. The bottom of the shaft would then fill
with water as the natural underground water seeped in through
the walls and floor. Steps were then hewn into the side of
the shaft, often in a spiral, from the ground level to below
the water level. A person requiring immersion would descend
into this "well" and immerse there. A mikva in Friedburg,
Germany, went down more than 60 feet (18 meters)!
In the last few centuries a new type of mikva was
constructed, one that is situated above or level with the
ground surface yet which remains faithful to all the laws
governing the underground version. Up until a few decades ago
these mikvas were filled by gathering rainwater and directing
it into the required pool. With the advent of modern boring
and pumping techniques it has now become possible to fill
these above ground mikvas with the natural water found
A mikva is a collection of 40 se'ah -- the greater
part of 1000 liters -- of suitable static water. Water is not
suitable if it:
1) Has been contained in or passed through a container not
built into the ground; or
2) Was propelled into the mikva by direct human energy.
There are many other laws and details pertaining to the
suitability of water and the construction of the pool, but
here we will focus only on these aspects, and how they were
dealt with in the "Be'er Chaya Esther" mikva recently
dedicated in Johannesburg, South Africa, where halachic
aspects were supervised by HaRav Meir Posen. Of course,
anyone actually wishing to construct a mikva should consult
with a competent authority and not rely on what is written
here for practical advice or recommendations since there are
often special considerations that apply in a given
The Modern Day Mikva
The water for the modern day mikva is obtained either by
collecting rain water or by drilling for subterranean water.
As we will see later on, once we have a kosher mikva from one
of these two sources it is possible to combine tap water with
either of them, but only according to certain strict
When obtaining our initial water either from rain or a
borehole, it is imperative that at no stage in the water's
journey from its source to its destination does it violate
either of the above two prerequisites. That is to say it must
not at any stage pass through a container not built into the
ground and it must also at no stage be propelled by direct
This is relatively simple when we are obtaining water from
the rain, since the water can be gathered directly into a
tank which was built into the ground and then piped directly
into the mikva through straight pipes (which are not
considered containers) using gravity to propel it from the
gathering tank into the mikva. When obtaining water from a
borehole, however, we run into some difficulties.
The Borehole Challenge
Water occurs naturally underground and is known as ground
water. This water accumulates chiefly from the rain that
filters through the soil. The water settles into the pores
and cracks of underground rocks and into the spaces between
grains of sand and pieces of gravel. A layer or bed of such
porous material that yields useful amounts of water is called
an aquifer. It is into this layer that a borehole is sunk.
The borehole usually takes the form of a long pipe which is
inserted into a hole drilled into the ground by a boring
drill, the end of this pipe being submerged in the aquifer.
In most cases, where a mikva is not involved, the water is
propelled up this pipe by attaching a pump to the bottom end
of the pipe and pumping the water up. However, when it comes
to building a mikva, this method of drawing the water up
cannot be used because it violates both of the abovementioned
First, even though the pipes themselves are not considered
containers, the pump is, and hence the water passes through a
container which is not connected to the ground. Thus the
water has violated our first prerequisite. Second, the water
is being propelled by energy initiated by a person in the
form of a pump and is not flowing naturally, thereby
violating our second prerequisite.
The Borehole Solution
The modern-day solution to this vexing problem lies in a
simple scientific phenomenon: a light liquid will rise to the
surface of a heavier liquid, the most common example of this
being oil and water. To illustrate how this relates to our
borehole, suppose one were to place a straw filed with oil
and plugged at the top, into a glass of water
When the stopper is removed, one would observe that the water
below the straw will force the oil in the straw upwards until
some of the oil cascades out the top of the straw
(Illustration B). This occurs because the oil within the
straw is lighter than the water on the outside and hence
needs to rise.
The same phenomenon would be observed if the straw were
filled with carbonated water, because the carbonated water is
saturated with gas and is, like the oil, lighter than the
water around the straw.
Based on the above, we will now be able to understand how it
is possible to draw up kosher mikva water from a borehole.
The solution, which may sound more complicated than it is in
practice, is to carbonate, or more accurately to aerate, the
water in the pipe so that, like with the straw, the water
below it will force the water in the pipe up to the surface.
This is done by pumping compressed air from a powerful
compressor (Illustration C) down a separate pipe to the base
of the water pipe, and bubbling this air into the water in
the pipe so that it gets aerated.
This method of raising the water satisfies both of our
requirements for kosher water because, first, it does not
pass through a container not built into the ground and
second, because it spurts to the surface on its own accord
and is not propelled by direct human energy. Only human
ingenuity is at work here.
Building A Functional Mikva
Having obtained suitable rain or ground water, we can now
simply direct it into an adequately-sized pool and we will
have a perfectly kosher mikva. There is however a practical
consideration to be dealt with, which obviously requires a
solution which is in accordance with the halacha: Were we to
use this single pool for the immersion itself, the water
would become dirty after some time and would need to be
replaced with either rain or borehole water, both of which
are not always readily available in suitable quantities.
There are two ways to overcome this technicality, both of
which are discussed extensively in the halachic texts. Both
involve connecting a pool of fresh tap water to an existing
kosher mikva in such a way that the new pool is rendered
kosher by the existing mikva. The two possible methods of
doing this are know as "Hashoka" (lit. "kissing") and
"Zriah" (lit. "planting").
The Mishna in Mikvo'os (6: 7,8) describes how
one can connect a mikva containing suitable water to one that
is unsuitable by touching their water together and thereby
make two kosher pools. The meeting point of the two waters
needs to be a minimum size of "the spout of a waterskin"
which was defined by the rabbis to be the width of the two
fingers closest to the thumb squared, and is taken to be
around 4.5 cm. squared.
Using this method we could fill the main mikva pool with
clean -- even heated -- tap water and then simply allow it to
touch (or "kiss") an existing kosher pool, known as the
Bor Hashoka and thereby validate the fresh pool of
water. This method allows us to keep one small pool of rain
or borehole water indefinitely, only replacing the main pool
at regular intervals with fresh tap water.
Once a mikva has the required 40 se'ah of water in it,
the halacha states that one can add all the water in the
world into this pool and it will not become unkosher. When
using the Zriah method based on this halacha, a kosher
mikva is built alongside an empty pool. Tap water is added
into the kosher mikva until the mixture overflows into the
empty pool. This second pool is used for immersions until
gets dirty. It is then emptied and the entire process can
then be repeated.
The process is named Zriah because one "plants" the
unsuitable water in the mikva like a seed placed in the
ground, and just as the grain becomes part of the ground so
too the suitable water becomes part of the kosher mikva. The
original kosher mikva in such a case is known as a Bor
This method once again allows us to keep one small pool of
rain or borehole water indefinitely, only refilling the main
pool (by overflowing tap water from the smaller pool) at
The above two methods are described and endorsed by the
Shulchan Oruch, the foremost authority when it comes
to halacha. Under normal circumstances, we would follow the
opinion of the Shulchan Oruch, even in the face of
more strict opinions. The laws of mikva however are not
normal circumstances, and about these laws the Tashbatz
writes that we should try "not to poke ones head between a
disagreement of the Rishonim." Thus one should rather take
the strictest view into account, when practical, in order to
satisfy all the opinions. It has been explained that the
reason why one should be exceptionally particular when it
comes to the laws of mikva, is because it is on these laws
that the purity of the entire Jewish nation depends.
There are two points about which some of the authorities
differ with the Shulchan Oruch and have more stringent
opinions. The first issue is one of dilution. All opinions
agree that as long as we have 40 se'ah of kosher
water, we can add all the water in the world into that pool
and the pool would still remain kosher.
There is however one condition, according to some opinions.
Supposing we had a kosher mikva containing exactly 40
se'ah. Into this pool we now add 80 se'ah of
tap water. All opinions agree that this mixture is kosher.
Now suppose someone removed a glass of water from this pool.
The water in the glass would be composed of about two-thirds
tap water and one-third mikva water. What we suddenly realize
is that our original 40 se'ah now lacks a third of a
glass, and the entire mixture becomes unsuitable. According
to these opinions (which, as we said, the Shulchan
Oruch does not follow), this problem undermines the
entire concept of Zriah, where we completely ignored
dilution and allowed the mixture to flow into the empty
Even when using Hashoka, there can also be a problem
of dilution. As someone enters the mikva, the water level
rises and then drops and the motion of the water will slowly
dilute the Bor Hashoka. When the main mikva is
emptied, we may find that our Bor Hashoka contains less than
40 se'ah of kosher water.
As we mentioned already, and we want to stress this, this is
a lone opinion -- primarily that of the Ra'avad -- which we
would not usually take into account. The Shulchan
Oruch's opinion on the above case would be that once we
have added the tap water into the mikva, we view the mixture
in its entirety and not as two separate components. Hence
when one removes the glass of water according to the
Shulchan Oruch, one has removed one glass of the
kosher mixture and not two-thirds of a glass tap water and
one-third kosher. Therefore, according to the Shulchan
Oruch, Zriah is a perfectly valid way of filling the
empty pool described above.
The second issue raised in the commentaries pertains to
Hashoka and when it can or cannot be used. There are
opinions which maintain that the mechanism of Hashoka
was not created to purify an entirely unsuitable mikva as
we proposed above but is rather a method of joining a kosher
mikva which lacks the correct volume of water to one that has
Applying These Stringencies To A Real
Due to the above issues and based on the idea that we should
take all opinions into account when building a mikva, various
approaches are taken. In dry climates, two separate pools, an
independent Bor Hashoka and Bor Zriah are used.
This approach was discussed by the Chazon Ish.
Another approach, that was used in the "Be'er Chaya Esther"
mikva that was officially opened in Johannesburg, South
Africa last week, is to construct the mikva in such a way
that we do not need to use tap water at any stage. The best
way of doing this is to fill the immersion pool itself with
borehole water. As an added stringency we also do a
Hashoka between this pool and a smaller pool which was
filled with rain water. This is done to counter the minute
chance that the borehole was rendered unsuitable.
Rain water could also be used to fill the main pool but it is
often dirty due to pollution in the atmosphere, and is not
always available in suitable quantities. In some mikvas, they
store rainwater and use some of it each time they refill the
It must be emphasized that we use these approaches only where
possible and that a mikva is one hundred percent kosher if it
was built as described in the Shulchan Oruch.
It is reported that the Chasam Sofer built a mikva relying
entirely on Zriah and that this mikva was only filled
with rain water once in its entire lifetime. Two mikvas were
dug alongside one another, the one was then filled with
rainwater and the other empty. Tap water was then introduced
into the full pool until it overflowed into the empty one.
One of the pools was then used for immersion until it became
dirty, whereupon it was emptied and refilled by pouring tap
water into its partner. After a short period of time, none of
the original water would have remained, but this mikva was
nevertheless perfectly kosher according to the Shulchan
The Chasam Sofer's reason for building such a mikva was that
the doctors in his town had recommended not to use the mikvas
because they were supposedly detrimental to one's health. The
Chasam Sofer knew that if he did not build mikvas containing
the finest quality water, the spiritual purity of his entire
town would be at stake. Hence he chose not to fulfill the
chumros. He does however write that if one can be more
stringent and use borehole water it is praiseworthy.