Building your own pool is not for everyone, but it can be done, with great results. When I got bids around $30,000 , the choice was to build it myself, or forget it.
For around $7000, and a lot of work, my son and I built a very solid 13' x 22' x5' oval concrete pool off our deck.
We built it on flat ground , but it could also be built in a hole and backfilled.
Keeping the plumbing simple also cut costs.
Block pools can have problems because they lacks the steel needed.
We used lintel block (normally used over doors and windows) to wrap rebar around the pool every 8 inches horizontally.
Stacking the blocks with cores lined up put a rebar vertically every 8 inches.
We cut the sides out of the base row of block to let rebar and concrete connect the wall and pool floor.
The result was a pool that could stay solid on the 3 ft. of rock backfill behind our retaining wall.
We plastered and waterproofed the pool ourselves with white surface bonding cement, and 2 years later hired a pro crew to do a finish coat of prettier blue cement plaster.
This pool had to be very strong, because it sits on backfill in an earthquake area next to the Sea of Cortez. The backfill was all rock, not dirt, which settles.
Block pools can have problems because they lack horizontal steel and they can leak where walls meet the floor.
Curved walls are much stronger than straight, so I chose an oval. I wanted #4 rebar every 8" vertical and horizontal in the walls and continuous through the floor. This is impossible with standard block, but lintel block has notches which let you add horizontal bars every 8"
We kept the pool 30" away from the retaining wall to allow access for plumbing and pump.
To use a small spa 1/2 hp pump we kept the 2"return and 1.25"supply lines large and close to the pump.
A cartridge filter completed the plumbing.
Waterproofing comes from the cement plaster inside a pool. Any crack in the structure means a leak, as the crack will continue through the plaster.
We used fiberglass reinforced plaster inside and out to hold the blocks solid until the concrete was poured cured. This alone waterproofed the pool.