Okay, now to the practicalities. Before installing a water feature you need to ask yourself several important questions first: What is your budget? How much can you spend on the entire project? You could spend $3,000 on a water feature and find out you still need an additional $1,000-1,500 for plants and amenities, such as a deck, gazebo, walkways, fish or landscape lighting in the pond, waterfall and lawn. Other possible extras are a biological filter, auto-fill for pond, skimmer, back-flushable bio-filter, and more. How big is a water feature? If you are building your own, then structurally size is not that big an issue! I would charge the same price for a 3-foot high waterfall as I would for a 5-foot; the same for a 3 by 5-foot pond as a 4 by 6. There is only a $200 difference in cost between the 1,000 and 2,000 square feet of concrete shell surface. Your main concern about size should be space, not cost.
How much of your yard can you sacrifice? Even if the space between your house and the property line fence is limited, a water feature can be incorporated. Small ponds 1 to 3 feet deep can facilitate a sump pump located within the pond. Even though a sump pump is inexpensive, it consumes much more energy than an above-ground pump.
A pond any deeper than 3 feet requires an exterior pump for better accessibility and maintenance, and at a higher cost. But they pay for themselves in a short period of time with the energy savings. Also, larger ponds require greater filtration, more cleaning and maintenance. The size of the waterfalls will determine the size of the pump needed. The higher the waterfalls, the bigger the pump needed to supply the water and the greater the cost for electricity. Height creates head pressure which requires more energy and is the major factor in operating cost. How much entertaining will you do? Will you need a deck? If so, how big? You might consider placing a pond next to an existing deck. Many people do just the opposite, they build a pond and then construct a deck beside it. In this case, you can take advantage of an existing deck and construct an open stairway (stair-bridge) to span the pond. This affords unique access to the opposite side.
Will you have adequate room for table and chairs? Do you want a spa? Or a fire pit or barbeque? Enough lawn for games? Where do you spend most of your outdoor leisure time? That is the area for your waterfall! The waterfall will bring you the most enjoyment, therefore it should be located closest to the area where you plan to spend most of your time out of doors.
Do you want to see or hear the waterfall from indoors? Consider adding an exterior patio or French doors to your house to access your water feature area. Do you wish to have fish and other aquatic creatures? Long term, a properly maintained nitrogen cycle costs less than maintaining a pond that uses chlorine and other chemicals.
Fish, plants and proper bacteria are needed for healthy pond and nitrogen cycle. Once properly established, a healthy fish pond is virtually maintenance free. Are you willing to remove or replace certain trees or bushes to enhance the waterfall and pond? Some trees have very aggressive root systems that can literally move concrete as they grow, causing cracking and upheaval.