Chapter 2: HOW POOLS WORK. How to Build Your Own Home Swimming Pool or Spa
As we said before, pools are essentially gigantic holes
in the ground, filled with water. But we
were being somewhat disingenuous in saying this, because the water in your pool
is doing much more than just sitting around waiting for swimmers to enjoy
it. In reality, the water in a swimming
pool is constantly active, flowing into and out of the pool through a complex
system of pipes and filters. A good
understanding of exactly how the water in your pool works is essential to
understanding why certain maintenance steps are essential to the health and
lifetime of your pool.
A pool without a drain is going to turn unsafe (and
frankly disgusting) very quickly.
Typically, a swimming pool has one or two main drains in addition to the
other more specialized drains we'll be talking about just below.
The main drains in a pool need to be placed at the
lowest point in the pool basin. Their
job is to get rid of all the heavy debris that collects in a pool--and you'd
better believe that there will be plenty of heavy debris that collects in a
pool. The debris exits the pool through
the main drains and passes through the pipe systems to the pool filter.
So you may have asked yourself: why two drains? The reason to install two main drains rather
than just one is to avoid serious safety issues. As anyone with a bathtub knows, water tends
to form a vortex when it drains quickly from a basin through a small
opening. In a typical swimming pool, the
amount of water being channeled through a drain is so high that the vortex
created can actually trap a child against the bottom of the pool, rendering
them unable to escape and quickly drowning them. This is obviously not the intended use for a
pool drain. So a second drain is usually
installed (along with all of the other types of drains in a typical swimming
pool) in order to reduce the total amount of water that needs to drain from a
single opening in the pool basin. Drains
should also be outfitted with "antivortex coverings", which help to
regulate pool drainage and prevent dangerous vortexes from forming.
Main drains help to clear all of the heavy debris from
a pool. Skimmer drains help to clear all
of the light debris that floats on the surface of a pool. This may seem like a minor or simply cosmetic
problem, but even over the space of one day a serious amount of debris can form
on the surface of the water in your pool, from fallen leaves to summer insects
to worse. The skimmer drain allows water
to sluice cleanly from the top of the pool through the skimmer basket,
filtering out large amounts of debris before it can enter the filtration
system.
Skimmer drains are usually equipped with a
"floating weir", which is a type of door that swings open and shut
depending on the amount of water pressing against it. When operating correctly, the floating weir
will swing open and admit only as much water as the drainage system can handle
into the pool's pipes.
Skimmer drains also have a secondary access pipe in
addition to the drain leading to the filtration system. This is called the "equalizer
line", and it connects to the main basin of the pool somewhere below the
water line. If the water level in the
pool drops below the level of the floating weir due to extra heat, regular
maintenance, or for any other cause, this allows the pool to continue to draw
only water through the skimmer basket line and avoids any air being pulled into
the filtration system (which causes obvious problems.) The equalizer line needs to be outfitted with
an antivortex covering, just like the main drains.
The water doesn't travel through the drain by gravity
and water pressure alone. In order to
make the pool run efficiently, an electrical pump system needs to be used.
The pump system is simply a small pump casing connected
to the various drains and pipes that service the pool. It's usually kept out of sight from the rest
of the pool, in part because it's not really appealing to look at (similar to
the reason human internal organs are kept inside the body, not outside) and in
part because keeping the pump out of sight also keeps it safe (ditto with human
internal organs.)
Pumps need to be outfitted with strainer baskets that
catch incoming debris before it reaches the actual filters. A good skimmer basket and drain covers will
go a long way toward catching debris before it can cause you any trouble, but a
strainer basket is necessary as a "last line of defense." Part of swimming pool maintenance involves
emptying and cleaning the strainer basket regularly.
When the water leaves the pool through the drains, it
needs to pass through a filtration system. This purifies the water by pulling out debris
and allows clean water to return to the pool, keeping the pH balance stable and
keeping the water from getting cloudy.
The filter system in a pool is fairly large and is
usually kept above ground for easy access and maintenance. It looks something like a gigantic metal urn
connected to various pipes.
There are several different types of filters. One of the simplest is a sand filter. When dirty water comes into the filtration
system from the drains, pressure forces the water to travel down through the
sand. The sand traps dirt and debris and
leaves the exiting water clean.
Bear in mind the following caveat: even though it's
called a sand filter, you can't simply pour any old sand into the filter and
hope for the best. Only use specialized
sand bought from a trusted pool supply store or other supplier. This sand will have a special square-crystal
shape, designed for use in pool filtration.
This should go without saying, but as you know, installing a pool is a
major financial investment--better to be safe than sorry.
The two other major types of filters are diatomaceous
earth filters and cartridge filters.
Diatomaceous earth filters contain special grids lined with
"diatomaceous earth", which are essentially the tiny skeletons of sea
creatures known as "diatoms" mixed with regular sand. Diatomaceous earth is slightly more
expensive, but filters pools more effectively and can be easier to maintain. Cartridge filters are exactly what they sound
like: long plastic casings lined with cloth or other straining materials. Cartridge filters do a better job of cleaning
debris from pool water, but will require regular replacement in addition to
"backwashing" maintenance (which we'll cover shortly.)
Once water leaves the filter, it can go to one of two
places. One is the city sewer
system. The other is the pool. The return valve is the connection from the
bottom of the filter tank (where clean water collects) to the pool itself.
Return valves also generate a great deal of suction
during use, and should be covered by antivortex coverings if possible. Ideally your pool will have more than one
return valve to minimize any problems caused by vortex formation. Return valves are the tiny "jets"
that come out of the side of the pool, and any kids using the pool should be
warned not to block the water flowing in through the "jets" in order
to avoid any problems with creating extra suction in the filtration system. (Again, this seems like common sense, but for
some reason kids naturally love to block off the return valves in a pool--if we
all knew why kids take such pleasure in this, we'd no doubt be a lot happier in
our adulthood than we are.)
There are two other fixtures that you'll want to have
in your pool. Although these aren't as
essential to making your pool work, they're still nice things to have and save
you a lot of work in regular maintenance.
One is a connection to refill the pool with fresh water
from the city water supply. You can in
theory refill a pool with any source of fresh water (garden hoses, bearing jars
one by one from a local well), but having a direct connection to the water
supply in the pool itself saves you plenty of work when you'll inevitably need
to replenish some of the water supply in your pool. This can happen due to simple use (water
splashing onto the pool deck, water carried out on the body when exiting the
pool, pool water used to fill a squirt gun or other toy) or due to underlying
conditions (strong heat causing pool water to evaporate.) It's worth the time and extra expense to
simply install this connection when you install the pool itself.
The other optional but vital fixture in a pool is the
vacuum port. This is used to attach pool
vacuum cleaners to the filtration system of the pool.
Hold on, you may be thinking. I already have all of these fancy drains to
catch debris and dirt on the bottom of the water as well as on the
surface. Why should I need to have a
vacuum cleaner as well?
The answer is simply that as efficient as your main
drains and skimmers are, they can't catch every little bit of dirt and
debris. If you have a concrete pool in
particular, lots of dirt will collect in the rough patches of concrete or
plaster that line the pool basin. The
drain could handle this dirt if the dirt ever made it to the drain, but it
usually remains trapped along the side of the pool, where it makes the concrete
look shabby and unappealing.
There are two options for cleaning it. One is to take a brush, dislodge all of the
dirt, and hope for the best. The other
is to use a vacuum cleaner which can stay in the pool all the time, snaking
along the surface, slowly picking up dirt, and passing it through to the filter
for disposal. It's slightly more
expensive and you'll need to perform some regular maintenance on the pool
vacuum, but in the long run you'll be spending some money to save lots of time
and effort: usually a good bargain.
One thing to watch out for when choosing a pool vacuum:
pay attention to how the pool vacuum works.
Some pool vacuums have their own on-board pumps and motors, while some
work by drawing suction power from the pool's main pump system. There are advantages and disadvantages to
both options.
Generally speaking, having an onboard pump for a pool
vacuum is probably the better idea, since it puts less overall stress on your
pool and ensures that if there's a problem with your pump system, you can at
least keep the pool somewhat clean while the problem is being fixed.
Having an onboard pump involves some extra maintenance
on your part, however, and probably some ongoing costs in terms of keeping the
vacuum motor/pump assembly powered and operating. As long as you have some kind of vacuum,
though, you'll be saving yourself immeasurably more work in terms of general
maintenance than you'll be spending on the vacuum assembly itself.
These are in no way essential, but there are extra
options to make your pool experience more enjoyable that you might to think
about when choosing and installing your pool.
These can include slides, spas, bench seating, step or ladder exits, and
diving boards.
Generally these options don't involve much in the way
of additional maintenance (except, of course, for spas, which we'll talk about
in a later chapter.) When choosing bells
and whistles for your pool, the most prudent thing to think about is
safety. Some kind of pool exit is a must
to prevent people from injuring themselves by slipping when they're climbing
out of a pool along the side.
Ladders are a cheap option, but bench seatings or
molded steps are usually safer and more visually attractive. Any extra molding you put into your pool
basin will give dirt and debris more of a chance to collect, however, and will
cost you more in terms of overall maintenance time. Usually the extra enjoyment you'll get out of
the pool will offset this extra maintenance, but it's still a good idea to be
aware of these things before the gigantic hole is dug in your backyard (as I'm
sure you'd agree.
Essentially, that's all there is to the functioning
parts of a pool. There's just one big
issue in keeping your pool working that we need to cover before moving on to
actual maintenance issues: the major issue of water quality.
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