A reverse osmosis filtration system (100; 500) comprising: a water-on-water storage tank (102; 502) comprising a squeeze side (106; 506) and a product side (108; 508) separated by a membrane; a filter module in fluid communication with the water-on-water storage tank (102; 502), a feed source, a product outlet (144; 544), and a drain outlet (142; 542), wherein the filter module comprises a reverse osmosis filter (132; 532); a feed line connecting the feed source to a feed inlet of the filter module; a product line connecting a filtrate outlet of the filter module to the product side (108; 508) of the storage tank (102; 502) and the product outlet (144; 544); and a drain line (135; 535) connecting a reject outlet (133; 533) of the filter module to the squeeze side (106; 506) of the storage tank (102; 502) and the drain outlet (142; 542) of the system; and a shuttle valve (105; 205; 505) that regulates the flow from the feed source, wherein the shuttle valve (105; 205; 505) comprises a piston body (710; 810) in a housing, the piston body (710; 810) having a first end portion connected to a spring and a second end portion, wherein pressure in the product line on the second end portion determines the state of the shuttle valve (105; 205; 505), wherein the piston body (710; 810) has a diameter that is substantially the same along its length, wherein the piston body (710; 810) comprises a plurality of sections, a first group of sections each independently having a solid surface effective to block flow from or to one or more of the following: a valve feed inlet port (116; 216; 516), a valve feed outlet port (118; 218; 518), a drain port (124; 224; 524), a reject port (120; 220; 520), and a tank squeeze port (122; 222; 522) depending on the state of the shuttle valve (105; 205; 505), and a second group of sections each independently having a plurality of channels (750; 850) effective to permit flow from or to one or more of the following: the valve feed inlet port (116; 216; 516), the valve feed outlet port (118; 218; 518), the drain port (124; 224; 524), the reject port (120; 220; 520), and the tank squeeze port (122; 222; 522) depending on the state of the valve (105; 205; 505), wherein the channels (750; 850) independently comprise linear grating or spiral grating to define the channels (750; 850). a water-on-water storage tank (102; 502) comprising a squeeze side (106; 506) and a product side (108; 508) separated by a membrane; a filter module in fluid communication with the water-on-water storage tank (102; 502), a feed source, a product outlet (144; 544), and a drain outlet (142; 542), wherein the filter module comprises a reverse osmosis filter (132; 532); a feed line connecting the feed source to a feed inlet of the filter module; a product line connecting a filtrate outlet of the filter module to the product side (108; 508) of the storage tank (102; 502) and the product outlet (144; 544); and a drain line (135; 535) connecting a reject outlet (133; 533) of the filter module to the squeeze side (106; 506) of the storage tank (102; 502) and the drain outlet (142; 542) of the system; and a shuttle valve (105; 205; 505) that regulates the flow from the feed source, wherein the shuttle valve (105; 205; 505) comprises a piston body (710; 810) in a housing, the piston body (710; 810) having a first end portion connected to a spring and a second end portion, wherein pressure in the product line on the second end portion determines the state of the shuttle valve (105; 205; 505), wherein the piston body (710; 810) has a diameter that is substantially the same along its length, wherein the piston body (710; 810) comprises a plurality of sections, a first group of sections each independently having a solid surface effective to block flow from or to one or more of the following: a valve feed inlet port (116; 216; 516), a valve feed outlet port (118; 218; 518), a drain port (124; 224; 524), a reject port (120; 220; 520), and a tank squeeze port (122; 222; 522) depending on the state of the shuttle valve (105; 205; 505), and a second group of sections each independently having a plurality of channels (750; 850) effective to permit flow from or to one or more of the following: the valve feed inlet port (116; 216; 516), the valve feed outlet port (118; 218; 518), the drain port (124; 224; 524), the reject port (120; 220; 520), and the tank squeeze port (122; 222; 522) depending on the state of the valve (105; 205; 505), wherein the channels (750; 850) independently comprise linear grating or spiral grating to define the channels (750; 850).