This is a very important question that may affect the cost of your fountain. On most commercial fountains the backwash water must go to sanitary sewer and not to storm sewer. In some municipalities these sewers are combined, so check with the building departments prior to designing the piping.
In either case, there must be an air gap between the pressurized backwash pipe from the filter and the sanitary sewer. This is usually accomplished by discharging the backwash pipe into a tank that then has a sanitary connection in the bottom of the tank. We usually size the backwash tank to accept the entire compliment of backwash water from the filter that is, the filter flow x 3 minutes.
There are two basic filter types that are used for fountains.
- A sand filter uses a bed of uniform size sand to pass the water through from top to bottom and when the sand gets dirty you rinse it out (called backwashing). When you backwash, you flush a certain amount of the water in the fountain away so the volume of the fountain would have an impact on the type of filter you use.
- A cartridge filter utilizes a material often paper or polypropylene that filters out dirt and particulate. When you clean it, you don’t have to flush it but you do have to take it out of its housing and wash it off. This takes longer than backwashing and while it still uses some water, it does not use as much as backwashing.
You don’t necessarily need a filter. Many smaller fountains are run with just a submersible pump and when the water gets dirty or cloudy, the water is drained and refilled. While this might be ok for small basins of water but it is not really practical for larger basins where the volume of water is more significant. Using a filter allows you to extend the interval between water changes and is a more practical way to keep the fountain maintained.
This is a question of both implementation and design. Fountains use water in the following ways:
- Based on their surface area and the climate that they are installed in, fountains have evaporation rates comparable to any other body of water like a lake or pond so they lose water based on their environment including wind, temperature and humidity.
- If a fountain has a waterfall, nozzles or other aerated display, this exposes more surface area to evaporation and can increase water use. The design of these elements within the fountain basin have to be well executed to contain overspray and splash without spraying or splashing outside of the basin and additional loss of water.
- When fountain filters are cleaned, the water in the filter tank is either drained to access the filter elements (in the case of cartridge filters and bag filters) or in the case of sand and DE filters the water is flushed through the filter tank at a high flow rate and sent to sewer. On large fountains with equally large filter systems, this can amount to significant amounts of water.
Note: While not always necessary, a backwashing system often provides benefits to the overall operation of the fountain. As water evaporates from the pools, the Total Dissolved Solids (TDS) increases because the minerals stay while the water leaves. Backwashing the filter removes some of that water which is replenished by the fill system, helping dilute the buildup of minerals in the water.
Whether fountains are a waste of water is a more subjective issue as for many years fountains were used as points of social