Influent Water Flow Control
Sample design and cost analysis
Family unit (probably approximately 7-10 people), have a tap, household use (drinking, cooking, cleaning, etc)
Because there is a tap, there would not be a need for a large holding tank since the tap can send the water directly into the filter. To control the flow of water through the filter, there will be a float valve on the top of the filter to maintain a constant level of water; this is important to maintain a height of water to maintain constant flow.
Family unit, don't have a tap, must pour water into holding tank, only filtering water for drinking and cooking, not cleaning
When the family unit does not have a tap, we will need to have a storage tank to hold the water. The water flows into the filter much like a tap water source. Again, there will be a float valve in the filter to maintain a constant level of water.
Sample holding tank cost: $34 for a 15 gallon tank from Baytec Containers
Apartment building size (approximately 50 people), tap, all uses
Again, since there is a tap, there would not be a need for a storage tank; the tap connects directly to the filter.
Business or school, have tap, not all uses- just cooking and drinking water, cleaning (but not showering)
No holding tank is needed.
Small village, no tap, bringing filter directly to river where individuals dump buckets of water into holding tank, only filtering water for drinking and cooking
Here, a large holding tank will be needed. Villagers will bring buckets of water to the holding tank where it will be filtered for the purposes of drinking and cooking, not cleaning. Because the water will not be used for sanitation and hygiene, we assumed the water consumption to be close to the absolute minimum for drinking water (approximately 5L per person per day).
Sample holding tank costs: Ace/DenHartog 55 Gallon Vertical NSF-61 Tank: $75.99
http://www.tank-depot.com/productdetails.aspx?part=A-VT0055-20 
Figure 1: Schematic of inlet with a holding tankFor cases 1, 3, 3.5 and 4:
Because there is no holding tank, the primary costs will come from the alum doser and the actual filter apparatus.
The height of water above the foam to get a velocity of 4mm/s:
Q=vc*Aor*sqrt(2gh)
Aor=Q/(vc*sqrt(2gh))
If we set the height of the water above the filter as 2in (0.0508m) and a lower, more conservative flow rate of 4mm/s:
Aor=(4*10-3)/(0.62*sqrt(2*9.81*(0.0508+0.254))
Aor=24.4m2
Implementing an alum doser:
To dose the influent water with alum, we can implement a flow controller for dosing alum prior to where the water enters the filter (with tap) or holding tank (without tap). As the raw water is entering, the flow controller will be dosing the water with a specific amount of alum; the alum and raw water will undergo rapid mixing prior to entering the filter or holding tank. In order to dose a specific amount of alum, we need a method to change the flow in using a method that does not require trial and error (ie. packets of alum) and something that controls the level of the liquid to achieve a constant pressure and flow. To achieve this, we can use the following design. A small bottle connects the alum stock to the rest of the filter. A float valve inside the bottle is used to maintain a constant alum level. Implementing a linear flow orifice meter that connects to the small bottle can help us choose the specific amount of alum dose that we want. This is achieved by drilling holes into a PVC entrance pipe connecting the alum doser to the raw water line. The hole you choose will change the amount of alum entering the raw water. The fluid level in the bottle should be the same level as the 0 cm mark on the pipe. The distance from the fluid level in the bottle (in cm) will be marked on each hole going down the pipe. However, a linear orifice meter may not be needed if we just want a constant flow of alum. The costs for implementing the flow controller can be found and adjusted from the online flow controller parts list.