I wouldn't call my pond just a "water feature". It contains a large number of goldfish, a dozen golden orfes, one large catfish and a dozen or so painted turtles. I'm a biologist who has worked at developing a pond that is a mature, well-balanced ecosystem that uses a large settling tank to remove solids, aeration from a waterfall in the summer and a bubbler in the winter, large surface area filters, and numerous submergent, emergent and floating plants to maintain the balance. Bacteria do a wonderful job of maintaining stable conditions. The settling tank is an above-ground pool where I grow water lilies that would otherwise be eaten by my turtles. Is is roughly a tenth of the volume of my pond and it gets drained each fall to flush out the accumulated detritus that is continually pumped from the bottom of the pond. It is refilled then, each spring, so I guess you could consider that, along with rainfall and snowmelt, to be a water change. I'm of the opinion that doing regular, significant, deliberate water changes (such as 10 to 20% per week as some do) is counterproductive as it sets the pond balance back. It takes some 3 years for a pond to establish a good balance and the worst case scenario is when people do not include bottom drains in the pond design, drain the pond each spring, power wash and refill. This is tantamount creating a brand-new pond each year and destroying the balance that was developing the year prior. Philosophies (and budgets) for maintaining a pond differ greatly and, just like a**holes, everyone has one. My opinion is that the almost OCD attitude about pond "cleanliness" and water clarity taken by many koi raisers borders on insanity. I'm also of the opinion that what works for you can be very different from what works for someone else. Do what makes you happy with your hobby and what you can afford. If you paid what I have to pay for water on a pension, you'd look for something other than water changes to maintain the health of your pond and fish. Biology is my answer.